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How fio works
The first step in getting fio to simulate a desired I/O workload, is writing a
job file describing that specific setup. A job file may contain any number of
threads and/or files -- the typical contents of the job file is a *global*
section defining shared parameters, and one or more job sections describing the
jobs involved. When run, fio parses this file and sets everything up as
described. If we break down a job from top to bottom, it contains the following
basic parameters:
`I/O type`_
Defines the I/O pattern issued to the file(s). We may only be reading
sequentially from this file(s), or we may be writing randomly. Or even
mixing reads and writes, sequentially or randomly.
Should we be doing buffered I/O, or direct/raw I/O?
`Block size`_
In how large chunks are we issuing I/O? This may be a single value,
or it may describe a range of block sizes.
`I/O size`_
How much data are we going to be reading/writing.
`I/O engine`_
How do we issue I/O? We could be memory mapping the file, we could be
using regular read/write, we could be using splice, async I/O, or even
SG (SCSI generic sg).
`I/O depth`_
If the I/O engine is async, how large a queuing depth do we want to
`Target file/device`_
How many files are we spreading the workload over.
`Threads, processes and job synchronization`_
How many threads or processes should we spread this workload over.
The above are the basic parameters defined for a workload, in addition there's a
multitude of parameters that modify other aspects of how this job behaves.
Command line options
.. option:: --debug=type
Enable verbose tracing of various fio actions. May be ``all`` for all types
or individual types separated by a comma (e.g. ``--debug=file,mem`` will
enable file and memory debugging). Currently, additional logging is
available for:
Dump info related to processes.
Dump info related to file actions.
Dump info related to I/O queuing.
Dump info related to memory allocations.
Dump info related to blktrace setup.
Dump info related to I/O verification.
Enable all debug options.
Dump info related to random offset generation.
Dump info related to option matching and parsing.
Dump info related to disk utilization updates.
Dump info only related to job number x.
Dump info only related to mutex up/down ops.
Dump info related to profile extensions.
Dump info related to internal time keeping.
Dump info related to networking connections.
Dump info related to I/O rate switching.
Dump info related to log compress/decompress.
*?* or *help*
Show available debug options.
.. option:: --parse-only
Parse options only, don\'t start any I/O.
.. option:: --output=filename
Write output to file `filename`.
.. option:: --bandwidth-log
Generate aggregate bandwidth logs.
.. option:: --minimal
Print statistics in a terse, semicolon-delimited format.
.. option:: --append-terse
Print statistics in selected mode AND terse, semicolon-delimited format.
**deprecated**, use :option:`--output-format` instead to select multiple
.. option:: --output-format=type
Set the reporting format to `normal`, `terse`, `json`, or `json+`. Multiple
formats can be selected, separate by a comma. `terse` is a CSV based
format. `json+` is like `json`, except it adds a full dump of the latency
.. option:: --terse-version=type
Set terse version output format (default 3, or 2 or 4).
.. option:: --version
Print version info and exit.
.. option:: --help
Print this page.
.. option:: --cpuclock-test
Perform test and validation of internal CPU clock.
.. option:: --crctest=test
Test the speed of the builtin checksumming functions. If no argument is
given, all of them are tested. Or a comma separated list can be passed, in
which case the given ones are tested.
.. option:: --cmdhelp=command
Print help information for `command`. May be ``all`` for all commands.
.. option:: --enghelp=[ioengine[,command]]
List all commands defined by :option:`ioengine`, or print help for `command`
defined by :option:`ioengine`. If no :option:`ioengine` is given, list all
available ioengines.
.. option:: --showcmd=jobfile
Turn a job file into command line options.
.. option:: --readonly
Turn on safety read-only checks, preventing writes. The ``--readonly``
option is an extra safety guard to prevent users from accidentally starting
a write workload when that is not desired. Fio will only write if
`rw=write/randwrite/rw/randrw` is given. This extra safety net can be used
as an extra precaution as ``--readonly`` will also enable a write check in
the I/O engine core to prevent writes due to unknown user space bug(s).
.. option:: --eta=when
When real-time ETA estimate should be printed. May be `always`, `never` or
.. option:: --eta-newline=time
Force a new line for every `time` period passed.
.. option:: --status-interval=time
Force full status dump every `time` period passed.
.. option:: --section=name
Only run specified section in job file. Multiple sections can be specified.
The ``--section`` option allows one to combine related jobs into one file.
E.g. one job file could define light, moderate, and heavy sections. Tell
fio to run only the "heavy" section by giving ``--section=heavy``
command line option. One can also specify the "write" operations in one
section and "verify" operation in another section. The ``--section`` option
only applies to job sections. The reserved *global* section is always
parsed and used.
.. option:: --alloc-size=kb
Set the internal smalloc pool to this size in kb (def 1024). The
``--alloc-size`` switch allows one to use a larger pool size for smalloc.
If running large jobs with randommap enabled, fio can run out of memory.
Smalloc is an internal allocator for shared structures from a fixed size
memory pool. The pool size defaults to 16M and can grow to 8 pools.
NOTE: While running :file:`.fio_smalloc.*` backing store files are visible
in :file:`/tmp`.
.. option:: --warnings-fatal
All fio parser warnings are fatal, causing fio to exit with an
.. option:: --max-jobs=nr
Maximum number of threads/processes to support.
.. option:: --server=args
Start a backend server, with `args` specifying what to listen to.
See `Client/Server`_ section.
.. option:: --daemonize=pidfile
Background a fio server, writing the pid to the given `pidfile` file.
.. option:: --client=hostname
Instead of running the jobs locally, send and run them on the given host or
set of hosts. See `Client/Server`_ section.
.. option:: --remote-config=file
Tell fio server to load this local file.
.. option:: --idle-prof=option
Report cpu idleness on a system or percpu basis
``--idle-prof=system,percpu`` or
run unit work calibration only ``--idle-prof=calibrate``.
.. option:: --inflate-log=log
Inflate and output compressed log.
.. option:: --trigger-file=file
Execute trigger cmd when file exists.
.. option:: --trigger-timeout=t
Execute trigger at this time.
.. option:: --trigger=cmd
Set this command as local trigger.
.. option:: --trigger-remote=cmd
Set this command as remote trigger.
.. option:: --aux-path=path
Use this path for fio state generated files.
Any parameters following the options will be assumed to be job files, unless
they match a job file parameter. Multiple job files can be listed and each job
file will be regarded as a separate group. Fio will :option:`stonewall`
execution between each group.
Job file format
As previously described, fio accepts one or more job files describing what it is
supposed to do. The job file format is the classic ini file, where the names
enclosed in [] brackets define the job name. You are free to use any ASCII name
you want, except *global* which has special meaning. Following the job name is
a sequence of zero or more parameters, one per line, that define the behavior of
the job. If the first character in a line is a ';' or a '#', the entire line is
discarded as a comment.
A *global* section sets defaults for the jobs described in that file. A job may
override a *global* section parameter, and a job file may even have several
*global* sections if so desired. A job is only affected by a *global* section
residing above it.
The :option:`--cmdhelp` option also lists all options. If used with an `option`
argument, :option:`--cmdhelp` will detail the given `option`.
See the `examples/` directory for inspiration on how to write job files. Note
the copyright and license requirements currently apply to `examples/` files.
So let's look at a really simple job file that defines two processes, each
randomly reading from a 128MiB file:
.. code-block:: ini
; -- start job file --
; -- end job file --
As you can see, the job file sections themselves are empty as all the described
parameters are shared. As no :option:`filename` option is given, fio makes up a
`filename` for each of the jobs as it sees fit. On the command line, this job
would look as follows::
$ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
Let's look at an example that has a number of processes writing randomly to
.. code-block:: ini
; -- start job file --
; -- end job file --
Here we have no *global* section, as we only have one job defined anyway. We
want to use async I/O here, with a depth of 4 for each file. We also increased
the buffer size used to 32KiB and define numjobs to 4 to fork 4 identical
jobs. The result is 4 processes each randomly writing to their own 64MiB
file. Instead of using the above job file, you could have given the parameters
on the command line. For this case, you would specify::
$ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
When fio is utilized as a basis of any reasonably large test suite, it might be
desirable to share a set of standardized settings across multiple job files.
Instead of copy/pasting such settings, any section may pull in an external
:file:`filename.fio` file with *include filename* directive, as in the following
; -- start job file including.fio --
include glob-include.fio
include test-include.fio
; -- end job file including.fio --
.. code-block:: ini
; -- start job file glob-include.fio --
; -- end job file glob-include.fio --
.. code-block:: ini
; -- start job file test-include.fio --
; -- end job file test-include.fio --
Settings pulled into a section apply to that section only (except *global*
section). Include directives may be nested in that any included file may contain
further include directive(s). Include files may not contain [] sections.
Environment variables
Fio also supports environment variable expansion in job files. Any sub-string of
the form ``${VARNAME}`` as part of an option value (in other words, on the right
of the '='), will be expanded to the value of the environment variable called
`VARNAME`. If no such environment variable is defined, or `VARNAME` is the
empty string, the empty string will be substituted.
As an example, let's look at a sample fio invocation and job file::
$ SIZE=64m NUMJOBS=4 fio jobfile.fio
.. code-block:: ini
; -- start job file --
; -- end job file --
This will expand to the following equivalent job file at runtime:
.. code-block:: ini
; -- start job file --
; -- end job file --
Fio ships with a few example job files, you can also look there for inspiration.
Reserved keywords
Additionally, fio has a set of reserved keywords that will be replaced
internally with the appropriate value. Those keywords are:
The architecture page size of the running system.
Megabytes of total memory in the system.
Number of online available CPUs.
These can be used on the command line or in the job file, and will be
automatically substituted with the current system values when the job is
run. Simple math is also supported on these keywords, so you can perform actions
and get that properly expanded to 8 times the size of memory in the machine.
Job file parameters
This section describes in details each parameter associated with a job. Some
parameters take an option of a given type, such as an integer or a
string. Anywhere a numeric value is required, an arithmetic expression may be
used, provided it is surrounded by parentheses. Supported operators are:
- addition (+)
- subtraction (-)
- multiplication (*)
- division (/)
- modulus (%)
- exponentiation (^)
For time values in expressions, units are microseconds by default. This is
different than for time values not in expressions (not enclosed in
parentheses). The following types are used:
Parameter types
String. This is a sequence of alpha characters.
Integer with possible time suffix. In seconds unless otherwise
specified, use e.g. 10m for 10 minutes. Accepts s/m/h for seconds, minutes,
and hours, and accepts 'ms' (or 'msec') for milliseconds, and 'us' (or
'usec') for microseconds.
.. _int:
Integer. A whole number value, which may contain an integer prefix
and an integer suffix:
[*integer prefix*] **number** [*integer suffix*]
The optional *integer prefix* specifies the number's base. The default
is decimal. *0x* specifies hexadecimal.
The optional *integer suffix* specifies the number's units, and includes an
optional unit prefix and an optional unit. For quantities of data, the
default unit is bytes. For quantities of time, the default unit is seconds.
With :option:`kb_base` =1000, fio follows international standards for unit
prefixes. To specify power-of-10 decimal values defined in the
International System of Units (SI):
* *Ki* -- means kilo (K) or 1000
* *Mi* -- means mega (M) or 1000**2
* *Gi* -- means giga (G) or 1000**3
* *Ti* -- means tera (T) or 1000**4
* *Pi* -- means peta (P) or 1000**5
To specify power-of-2 binary values defined in IEC 80000-13:
* *k* -- means kibi (Ki) or 1024
* *M* -- means mebi (Mi) or 1024**2
* *G* -- means gibi (Gi) or 1024**3
* *T* -- means tebi (Ti) or 1024**4
* *P* -- means pebi (Pi) or 1024**5
With :option:`kb_base` =1024 (the default), the unit prefixes are opposite
from those specified in the SI and IEC 80000-13 standards to provide
compatibility with old scripts. For example, 4k means 4096.
For quantities of data, an optional unit of 'B' may be included
(e.g., 'kB' is the same as 'k').
The *integer suffix* is not case sensitive (e.g., m/mi mean mebi/mega,
not milli). 'b' and 'B' both mean byte, not bit.
Examples with :option:`kb_base` =1000:
* *4 KiB*: 4096, 4096b, 4096B, 4ki, 4kib, 4kiB, 4Ki, 4KiB
* *1 MiB*: 1048576, 1mi, 1024ki
* *1 MB*: 1000000, 1m, 1000k
* *1 TiB*: 1099511627776, 1ti, 1024gi, 1048576mi
* *1 TB*: 1000000000, 1t, 1000m, 1000000k
Examples with :option:`kb_base` =1024 (default):
* *4 KiB*: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB
* *1 MiB*: 1048576, 1m, 1024k
* *1 MB*: 1000000, 1mi, 1000ki
* *1 TiB*: 1099511627776, 1t, 1024g, 1048576m
* *1 TB*: 1000000000, 1ti, 1000mi, 1000000ki
To specify times (units are not case sensitive):
* *D* -- means days
* *H* -- means hours
* *M* -- mean minutes
* *s* -- or sec means seconds (default)
* *ms* -- or *msec* means milliseconds
* *us* -- or *usec* means microseconds
If the option accepts an upper and lower range, use a colon ':' or
minus '-' to separate such values. See :ref:`irange <irange>`.
If the lower value specified happens to be larger than the upper value,
two values are swapped.
.. _bool:
Boolean. Usually parsed as an integer, however only defined for
true and false (1 and 0).
.. _irange:
Integer range with suffix. Allows value range to be given, such as
1024-4096. A colon may also be used as the separator, e.g. 1k:4k. If the
option allows two sets of ranges, they can be specified with a ',' or '/'
delimiter: 1k-4k/8k-32k. Also see :ref:`int <int>`.
A list of floating point numbers, separated by a ':' character.
.. option:: kb_base=int
Select the interpretation of unit prefixes in input parameters.
Inputs comply with IEC 80000-13 and the International
System of Units (SI). Use:
- power-of-2 values with IEC prefixes (e.g., KiB)
- power-of-10 values with SI prefixes (e.g., kB)
Compatibility mode (default). To avoid breaking old scripts:
- power-of-2 values with SI prefixes
- power-of-10 values with IEC prefixes
See :option:`bs` for more details on input parameters.
Outputs always use correct prefixes. Most outputs include both
side-by-side, like::
bw=2383.3kB/s (2327.4KiB/s)
If only one value is reported, then kb_base selects the one to use:
**1000** -- SI prefixes
**1024** -- IEC prefixes
.. option:: unit_base=int
Base unit for reporting. Allowed values are:
Use auto-detection (default).
Byte based.
Bit based.
With the above in mind, here follows the complete list of fio job parameters.
Job description
.. option:: name=str
ASCII name of the job. This may be used to override the name printed by fio
for this job. Otherwise the job name is used. On the command line this
parameter has the special purpose of also signaling the start of a new job.
.. option:: description=str
Text description of the job. Doesn't do anything except dump this text
description when this job is run. It's not parsed.
.. option:: loops=int
Run the specified number of iterations of this job. Used to repeat the same
workload a given number of times. Defaults to 1.
.. option:: numjobs=int
Create the specified number of clones of this job. Each clone of job
is spawned as an independent thread or process. May be used to setup a
larger number of threads/processes doing the same thing. Each thread is
reported separately; to see statistics for all clones as a whole, use
:option:`group_reporting` in conjunction with :option:`new_group`.
See :option:`--max-jobs`.
Time related parameters
.. option:: runtime=time
Tell fio to terminate processing after the specified period of time. It
can be quite hard to determine for how long a specified job will run, so
this parameter is handy to cap the total runtime to a given time. When
the unit is omitted, the value is given in seconds.
.. option:: time_based
If set, fio will run for the duration of the :option:`runtime` specified
even if the file(s) are completely read or written. It will simply loop over
the same workload as many times as the :option:`runtime` allows.
.. option:: startdelay=irange(time)
Delay start of job for the specified number of seconds. Supports all time
suffixes to allow specification of hours, minutes, seconds and milliseconds
-- seconds are the default if a unit is omitted. Can be given as a range
which causes each thread to choose randomly out of the range.
.. option:: ramp_time=time
If set, fio will run the specified workload for this amount of time before
logging any performance numbers. Useful for letting performance settle
before logging results, thus minimizing the runtime required for stable
results. Note that the ``ramp_time`` is considered lead in time for a job,
thus it will increase the total runtime if a special timeout or
:option:`runtime` is specified. When the unit is omitted, the value is
given in seconds.
.. option:: clocksource=str
Use the given clocksource as the base of timing. The supported options are:
Internal CPU clock source
cpu is the preferred clocksource if it is reliable, as it is very fast (and
fio is heavy on time calls). Fio will automatically use this clocksource if
it's supported and considered reliable on the system it is running on,
unless another clocksource is specifically set. For x86/x86-64 CPUs, this
means supporting TSC Invariant.
.. option:: gtod_reduce=bool
Enable all of the :manpage:`gettimeofday(2)` reducing options
(:option:`disable_clat`, :option:`disable_slat`, :option:`disable_bw_measurement`) plus
reduce precision of the timeout somewhat to really shrink the
:manpage:`gettimeofday(2)` call count. With this option enabled, we only do
about 0.4% of the :manpage:`gettimeofday(2)` calls we would have done if all
time keeping was enabled.
.. option:: gtod_cpu=int
Sometimes it's cheaper to dedicate a single thread of execution to just
getting the current time. Fio (and databases, for instance) are very
intensive on :manpage:`gettimeofday(2)` calls. With this option, you can set
one CPU aside for doing nothing but logging current time to a shared memory
location. Then the other threads/processes that run I/O workloads need only
copy that segment, instead of entering the kernel with a
:manpage:`gettimeofday(2)` call. The CPU set aside for doing these time
calls will be excluded from other uses. Fio will manually clear it from the
CPU mask of other jobs.
Target file/device
.. option:: directory=str
Prefix filenames with this directory. Used to place files in a different
location than :file:`./`. You can specify a number of directories by
separating the names with a ':' character. These directories will be
assigned equally distributed to job clones creates with :option:`numjobs` as
long as they are using generated filenames. If specific `filename(s)` are
set fio will use the first listed directory, and thereby matching the
`filename` semantic which generates a file each clone if not specified, but
let all clones use the same if set.
See the :option:`filename` option for escaping certain characters.
.. option:: filename=str
Fio normally makes up a `filename` based on the job name, thread number, and
file number. If you want to share files between threads in a job or several
jobs with fixed file paths, specify a `filename` for each of them to override
the default. If the ioengine is file based, you can specify a number of files
by separating the names with a ':' colon. So if you wanted a job to open
:file:`/dev/sda` and :file:`/dev/sdb` as the two working files, you would use
``filename=/dev/sda:/dev/sdb``. This also means that whenever this option is
specified, :option:`nrfiles` is ignored. The size of regular files specified
by this option will be :option:`size` divided by number of files unless
explicit size is specified by :option:`filesize`.
On Windows, disk devices are accessed as :file:`\\\\.\\PhysicalDrive0` for
the first device, :file:`\\\\.\\PhysicalDrive1` for the second etc.
Note: Windows and FreeBSD prevent write access to areas
of the disk containing in-use data (e.g. filesystems). If the wanted
`filename` does need to include a colon, then escape that with a ``\``
character. For instance, if the `filename` is :file:`/dev/dsk/foo@3,0:c`,
then you would use ``filename="/dev/dsk/foo@3,0\:c"``. The
:file:`-` is a reserved name, meaning stdin or stdout. Which of the two
depends on the read/write direction set.
.. option:: filename_format=str
If sharing multiple files between jobs, it is usually necessary to have fio
generate the exact names that you want. By default, fio will name a file
based on the default file format specification of
:file:`jobname.jobnumber.filenumber`. With this option, that can be
customized. Fio will recognize and replace the following keywords in this
The name of the worker thread or process.
The incremental number of the worker thread or process.
The incremental number of the file for that worker thread or
To have dependent jobs share a set of files, this option can be set to have
fio generate filenames that are shared between the two. For instance, if
:file:`testfiles.$filenum` is specified, file number 4 for any job will be
named :file:`testfiles.4`. The default of :file:`$jobname.$jobnum.$filenum`
will be used if no other format specifier is given.
.. option:: unique_filename=bool
To avoid collisions between networked clients, fio defaults to prefixing any
generated filenames (with a directory specified) with the source of the
client connecting. To disable this behavior, set this option to 0.
.. option:: opendir=str
Recursively open any files below directory `str`.
.. option:: lockfile=str
Fio defaults to not locking any files before it does I/O to them. If a file
or file descriptor is shared, fio can serialize I/O to that file to make the
end result consistent. This is usual for emulating real workloads that share
files. The lock modes are:
No locking. The default.
Only one thread or process may do I/O at a time, excluding all
Read-write locking on the file. Many readers may
access the file at the same time, but writes get exclusive access.
.. option:: nrfiles=int
Number of files to use for this job. Defaults to 1. The size of files
will be :option:`size` divided by this unless explicit size is specified by
:option:`filesize`. Files are created for each thread separately, and each
file will have a file number within its name by default, as explained in
:option:`filename` section.
.. option:: openfiles=int
Number of files to keep open at the same time. Defaults to the same as
:option:`nrfiles`, can be set smaller to limit the number simultaneous
.. option:: file_service_type=str
Defines how fio decides which file from a job to service next. The following
types are defined:
Choose a file at random.
Round robin over opened files. This is the default.
Finish one file before moving on to the next. Multiple files can
still be open depending on 'openfiles'.
Use a *Zipf* distribution to decide what file to access.
Use a *Pareto* distribution to decide what file to access.
Use a *Gaussian* (normal) distribution to decide what file to
For *random*, *roundrobin*, and *sequential*, a postfix can be appended to
tell fio how many I/Os to issue before switching to a new file. For example,
specifying ``file_service_type=random:8`` would cause fio to issue
8 I/Os before selecting a new file at random. For the non-uniform
distributions, a floating point postfix can be given to influence how the
distribution is skewed. See :option:`random_distribution` for a description
of how that would work.
.. option:: ioscheduler=str
Attempt to switch the device hosting the file to the specified I/O scheduler
before running.
.. option:: create_serialize=bool
If true, serialize the file creation for the jobs. This may be handy to
avoid interleaving of data files, which may greatly depend on the filesystem
used and even the number of processors in the system.
.. option:: create_fsync=bool
fsync the data file after creation. This is the default.
.. option:: create_on_open=bool
Don't pre-setup the files for I/O, just create open() when it's time to do
I/O to that file.
.. option:: create_only=bool
If true, fio will only run the setup phase of the job. If files need to be
laid out or updated on disk, only that will be done. The actual job contents
are not executed.
.. option:: allow_file_create=bool
If true, fio is permitted to create files as part of its workload. This is
the default behavior. If this option is false, then fio will error out if
the files it needs to use don't already exist. Default: true.
.. option:: allow_mounted_write=bool
If this isn't set, fio will abort jobs that are destructive (e.g. that write)
to what appears to be a mounted device or partition. This should help catch
creating inadvertently destructive tests, not realizing that the test will
destroy data on the mounted file system. Note that some platforms don't allow
writing against a mounted device regardless of this option. Default: false.
.. option:: pre_read=bool
If this is given, files will be pre-read into memory before starting the
given I/O operation. This will also clear the :option:`invalidate` flag,
since it is pointless to pre-read and then drop the cache. This will only
work for I/O engines that are seek-able, since they allow you to read the
same data multiple times. Thus it will not work on e.g. network or splice I/O.
.. option:: unlink=bool
Unlink the job files when done. Not the default, as repeated runs of that
job would then waste time recreating the file set again and again.
.. option:: unlink_each_loop=bool
Unlink job files after each iteration or loop.
.. option:: zonesize=int
Divide a file into zones of the specified size. See :option:`zoneskip`.
.. option:: zonerange=int
Give size of an I/O zone. See :option:`zoneskip`.
.. option:: zoneskip=int
Skip the specified number of bytes when :option:`zonesize` data has been
read. The two zone options can be used to only do I/O on zones of a file.
I/O type
.. option:: direct=bool
If value is true, use non-buffered I/O. This is usually O_DIRECT. Note that
ZFS on Solaris doesn't support direct I/O. On Windows the synchronous
ioengines don't support direct I/O. Default: false.
.. option:: atomic=bool
If value is true, attempt to use atomic direct I/O. Atomic writes are
guaranteed to be stable once acknowledged by the operating system. Only
Linux supports O_ATOMIC right now.
.. option:: buffered=bool
If value is true, use buffered I/O. This is the opposite of the
:option:`direct` option. Defaults to true.
.. option:: readwrite=str, rw=str
Type of I/O pattern. Accepted values are:
Sequential reads.
Sequential writes.
Sequential trims (Linux block devices only).
Random writes.
Random reads.
Random trims (Linux block devices only).
Sequential mixed reads and writes.
Random mixed reads and writes.
Sequential trim+write sequences. Blocks will be trimmed first,
then the same blocks will be written to.
Fio defaults to read if the option is not specified. For the mixed I/O
types, the default is to split them 50/50. For certain types of I/O the
result may still be skewed a bit, since the speed may be different. It is
possible to specify a number of I/O's to do before getting a new offset,
this is done by appending a ``:<nr>`` to the end of the string given. For a
random read, it would look like ``rw=randread:8`` for passing in an offset
modifier with a value of 8. If the suffix is used with a sequential I/O
pattern, then the value specified will be added to the generated offset for
each I/O. For instance, using ``rw=write:4k`` will skip 4k for every
write. It turns sequential I/O into sequential I/O with holes. See the
:option:`rw_sequencer` option.
.. option:: rw_sequencer=str
If an offset modifier is given by appending a number to the ``rw=<str>``
line, then this option controls how that number modifies the I/O offset
being generated. Accepted values are:
Generate sequential offset.
Generate the same offset.
``sequential`` is only useful for random I/O, where fio would normally
generate a new random offset for every I/O. If you append e.g. 8 to randread,
you would get a new random offset for every 8 I/O's. The result would be a
seek for only every 8 I/O's, instead of for every I/O. Use ``rw=randread:8``
to specify that. As sequential I/O is already sequential, setting
``sequential`` for that would not result in any differences. ``identical``
behaves in a similar fashion, except it sends the same offset 8 number of
times before generating a new offset.
.. option:: unified_rw_reporting=bool
Fio normally reports statistics on a per data direction basis, meaning that
reads, writes, and trims are accounted and reported separately. If this
option is set fio sums the results and report them as "mixed" instead.
.. option:: randrepeat=bool
Seed the random number generator used for random I/O patterns in a
predictable way so the pattern is repeatable across runs. Default: true.
.. option:: allrandrepeat=bool
Seed all random number generators in a predictable way so results are
repeatable across runs. Default: false.
.. option:: randseed=int
Seed the random number generators based on this seed value, to be able to
control what sequence of output is being generated. If not set, the random
sequence depends on the :option:`randrepeat` setting.
.. option:: fallocate=str
Whether pre-allocation is performed when laying down files.
Accepted values are:
Do not pre-allocate space.
Pre-allocate via :manpage:`posix_fallocate(3)`.
Pre-allocate via :manpage:`fallocate(2)` with
Backward-compatible alias for **none**.
Backward-compatible alias for **posix**.
May not be available on all supported platforms. **keep** is only available
on Linux. If using ZFS on Solaris this must be set to **none** because ZFS
doesn't support it. Default: **posix**.
.. option:: fadvise_hint=str
Use :manpage:`posix_fadvise(2)` to advise the kernel on what I/O patterns
are likely to be issued. Accepted values are:
Backwards-compatible hint for "no hint".
Backwards compatible hint for "advise with fio workload type". This
uses **FADV_RANDOM** for a random workload, and **FADV_SEQUENTIAL**
for a sequential workload.
Advise using **FADV_SEQUENTIAL**.
Advise using **FADV_RANDOM**.
.. option:: fadvise_stream=int
Use :manpage:`posix_fadvise(2)` to advise the kernel what stream ID the
writes issued belong to. Only supported on Linux. Note, this option may
change going forward.
.. option:: offset=int
Start I/O at the given offset in the file. The data before the given offset
will not be touched. This effectively caps the file size at `real_size -
offset`. Can be combined with :option:`size` to constrain the start and
end range that I/O will be done within.
.. option:: offset_increment=int
If this is provided, then the real offset becomes `offset + offset_increment
* thread_number`, where the thread number is a counter that starts at 0 and
is incremented for each sub-job (i.e. when :option:`numjobs` option is
specified). This option is useful if there are several jobs which are
intended to operate on a file in parallel disjoint segments, with even
spacing between the starting points.
.. option:: number_ios=int
Fio will normally perform I/Os until it has exhausted the size of the region
set by :option:`size`, or if it exhaust the allocated time (or hits an error
condition). With this setting, the range/size can be set independently of
the number of I/Os to perform. When fio reaches this number, it will exit
normally and report status. Note that this does not extend the amount of I/O
that will be done, it will only stop fio if this condition is met before
other end-of-job criteria.
.. option:: fsync=int
If writing to a file, issue a sync of the dirty data for every number of
blocks given. For example, if you give 32 as a parameter, fio will sync the
file for every 32 writes issued. If fio is using non-buffered I/O, we may
not sync the file. The exception is the sg I/O engine, which synchronizes
the disk cache anyway. Defaults to 0, which means no sync every certain
number of writes.
.. option:: fdatasync=int
Like :option:`fsync` but uses :manpage:`fdatasync(2)` to only sync data and
not metadata blocks. In Windows, FreeBSD, and DragonFlyBSD there is no
:manpage:`fdatasync(2)`, this falls back to using :manpage:`fsync(2)`.
Defaults to 0, which means no sync data every certain number of writes.
.. option:: write_barrier=int
Make every `N-th` write a barrier write.
.. option:: sync_file_range=str:val
Use :manpage:`sync_file_range(2)` for every `val` number of write
operations. Fio will track range of writes that have happened since the last
:manpage:`sync_file_range(2)` call. `str` can currently be one or more of:
So if you do ``sync_file_range=wait_before,write:8``, fio would use
writes. Also see the :manpage:`sync_file_range(2)` man page. This option is
Linux specific.
.. option:: overwrite=bool
If true, writes to a file will always overwrite existing data. If the file
doesn't already exist, it will be created before the write phase begins. If
the file exists and is large enough for the specified write phase, nothing
will be done.
.. option:: end_fsync=bool
If true, fsync file contents when a write stage has completed.
.. option:: fsync_on_close=bool
If true, fio will :manpage:`fsync(2)` a dirty file on close. This differs
from end_fsync in that it will happen on every file close, not just at the
end of the job.
.. option:: rwmixread=int
Percentage of a mixed workload that should be reads. Default: 50.
.. option:: rwmixwrite=int
Percentage of a mixed workload that should be writes. If both
:option:`rwmixread` and :option:`rwmixwrite` is given and the values do not
add up to 100%, the latter of the two will be used to override the
first. This may interfere with a given rate setting, if fio is asked to
limit reads or writes to a certain rate. If that is the case, then the
distribution may be skewed. Default: 50.
.. option:: random_distribution=str:float[,str:float][,str:float]
By default, fio will use a completely uniform random distribution when asked
to perform random I/O. Sometimes it is useful to skew the distribution in
specific ways, ensuring that some parts of the data is more hot than others.
fio includes the following distribution models:
Uniform random distribution
Zipf distribution
Pareto distribution
Normal (Gaussian) distribution
Zoned random distribution
When using a **zipf** or **pareto** distribution, an input value is also
needed to define the access pattern. For **zipf**, this is the `zipf
theta`. For **pareto**, it's the `Pareto power`. Fio includes a test
program, :command:`genzipf`, that can be used visualize what the given input
values will yield in terms of hit rates. If you wanted to use **zipf** with
a `theta` of 1.2, you would use ``random_distribution=zipf:1.2`` as the
option. If a non-uniform model is used, fio will disable use of the random
map. For the **gauss** distribution, a normal deviation is supplied as a
value between 0 and 100.
For a **zoned** distribution, fio supports specifying percentages of I/O
access that should fall within what range of the file or device. For
example, given a criteria of:
* 60% of accesses should be to the first 10%
* 30% of accesses should be to the next 20%
* 8% of accesses should be to to the next 30%
* 2% of accesses should be to the next 40%
we can define that through zoning of the random accesses. For the above
example, the user would do::
similarly to how :option:`bssplit` works for setting ranges and percentages
of block sizes. Like :option:`bssplit`, it's possible to specify separate
zones for reads, writes, and trims. If just one set is given, it'll apply to
all of them.
.. option:: percentage_random=int[,int][,int]
For a random workload, set how big a percentage should be random. This
defaults to 100%, in which case the workload is fully random. It can be set
from anywhere from 0 to 100. Setting it to 0 would make the workload fully
sequential. Any setting in between will result in a random mix of sequential
and random I/O, at the given percentages. Comma-separated values may be
specified for reads, writes, and trims as described in :option:`blocksize`.
.. option:: norandommap
Normally fio will cover every block of the file when doing random I/O. If
this option is given, fio will just get a new random offset without looking
at past I/O history. This means that some blocks may not be read or written,
and that some blocks may be read/written more than once. If this option is
used with :option:`verify` and multiple blocksizes (via :option:`bsrange`),
only intact blocks are verified, i.e., partially-overwritten blocks are
.. option:: softrandommap=bool
See :option:`norandommap`. If fio runs with the random block map enabled and
it fails to allocate the map, if this option is set it will continue without
a random block map. As coverage will not be as complete as with random maps,
this option is disabled by default.
.. option:: random_generator=str
Fio supports the following engines for generating
I/O offsets for random I/O:
Strong 2^88 cycle random number generator
Linear feedback shift register generator
Strong 64-bit 2^258 cycle random number generator
**tausworthe** is a strong random number generator, but it requires tracking
on the side if we want to ensure that blocks are only read or written
once. **LFSR** guarantees that we never generate the same offset twice, and
it's also less computationally expensive. It's not a true random generator,
however, though for I/O purposes it's typically good enough. **LFSR** only
works with single block sizes, not with workloads that use multiple block
sizes. If used with such a workload, fio may read or write some blocks
multiple times. The default value is **tausworthe**, unless the required
space exceeds 2^32 blocks. If it does, then **tausworthe64** is
selected automatically.
Block size
.. option:: blocksize=int[,int][,int], bs=int[,int][,int]
The block size in bytes used for I/O units. Default: 4096. A single value
applies to reads, writes, and trims. Comma-separated values may be
specified for reads, writes, and trims. A value not terminated in a comma
applies to subsequent types.
means 256k for reads, writes and trims.
means 8k for reads, 32k for writes and trims.
means 8k for reads, 32k for writes, and default for trims.
means default for reads, 8k for writes and trims.
means default for reads, 8k for writes, and default for writes.
.. option:: blocksize_range=irange[,irange][,irange], bsrange=irange[,irange][,irange]
A range of block sizes in bytes for I/O units. The issued I/O unit will
always be a multiple of the minimum size, unless
:option:`blocksize_unaligned` is set.
Comma-separated ranges may be specified for reads, writes, and trims as
described in :option:`blocksize`.
Example: ``bsrange=1k-4k,2k-8k``.
.. option:: bssplit=str[,str][,str]
Sometimes you want even finer grained control of the block sizes issued, not
just an even split between them. This option allows you to weight various
block sizes, so that you are able to define a specific amount of block sizes
issued. The format for this option is::
for as many block sizes as needed. So if you want to define a workload that
has 50% 64k blocks, 10% 4k blocks, and 40% 32k blocks, you would write::
Ordering does not matter. If the percentage is left blank, fio will fill in
the remaining values evenly. So a bssplit option like this one::
would have 50% 4k ios, and 25% 1k and 32k ios. The percentages always add up
to 100, if bssplit is given a range that adds up to more, it will error out.
Comma-separated values may be specified for reads, writes, and trims as
described in :option:`blocksize`.
If you want a workload that has 50% 2k reads and 50% 4k reads, while having
90% 4k writes and 10% 8k writes, you would specify::
.. option:: blocksize_unaligned, bs_unaligned
If set, fio will issue I/O units with any size within
:option:`blocksize_range`, not just multiples of the minimum size. This
typically won't work with direct I/O, as that normally requires sector
.. option:: bs_is_seq_rand
If this option is set, fio will use the normal read,write blocksize settings
as sequential,random blocksize settings instead. Any random read or write
will use the WRITE blocksize settings, and any sequential read or write will
use the READ blocksize settings.
.. option:: blockalign=int[,int][,int], ba=int[,int][,int]
Boundary to which fio will align random I/O units. Default:
:option:`blocksize`. Minimum alignment is typically 512b for using direct
I/O, though it usually depends on the hardware block size. This option is
mutually exclusive with using a random map for files, so it will turn off
that option. Comma-separated values may be specified for reads, writes, and
trims as described in :option:`blocksize`.
Buffers and memory
.. option:: zero_buffers
Initialize buffers with all zeros. Default: fill buffers with random data.
.. option:: refill_buffers
If this option is given, fio will refill the I/O buffers on every
submit. The default is to only fill it at init time and reuse that
data. Only makes sense if zero_buffers isn't specified, naturally. If data
verification is enabled, `refill_buffers` is also automatically enabled.
.. option:: scramble_buffers=bool
If :option:`refill_buffers` is too costly and the target is using data
deduplication, then setting this option will slightly modify the I/O buffer
contents to defeat normal de-dupe attempts. This is not enough to defeat
more clever block compression attempts, but it will stop naive dedupe of
blocks. Default: true.
.. option:: buffer_compress_percentage=int
If this is set, then fio will attempt to provide I/O buffer content (on
WRITEs) that compress to the specified level. Fio does this by providing a
mix of random data and a fixed pattern. The fixed pattern is either zeroes,
or the pattern specified by :option:`buffer_pattern`. If the pattern option
is used, it might skew the compression ratio slightly. Note that this is per
block size unit, for file/disk wide compression level that matches this
setting, you'll also want to set :option:`refill_buffers`.
.. option:: buffer_compress_chunk=int
See :option:`buffer_compress_percentage`. This setting allows fio to manage
how big the ranges of random data and zeroed data is. Without this set, fio
will provide :option:`buffer_compress_percentage` of blocksize random data,
followed by the remaining zeroed. With this set to some chunk size smaller
than the block size, fio can alternate random and zeroed data throughout the
I/O buffer.
.. option:: buffer_pattern=str
If set, fio will fill the I/O buffers with this pattern. If not set, the
contents of I/O buffers is defined by the other options related to buffer
contents. The setting can be any pattern of bytes, and can be prefixed with
0x for hex values. It may also be a string, where the string must then be
wrapped with ``""``, e.g.::
Also you can combine everything together in any order::
.. option:: dedupe_percentage=int
If set, fio will generate this percentage of identical buffers when
writing. These buffers will be naturally dedupable. The contents of the
buffers depend on what other buffer compression settings have been set. It's
possible to have the individual buffers either fully compressible, or not at
all. This option only controls the distribution of unique buffers.
.. option:: invalidate=bool
Invalidate the buffer/page cache parts for this file prior to starting
I/O if the platform and file type support it. Defaults to true.
This will be ignored if :option:`pre_read` is also specified for the
same job.
.. option:: sync=bool
Use synchronous I/O for buffered writes. For the majority of I/O engines,
this means using O_SYNC. Default: false.
.. option:: iomem=str, mem=str
Fio can use various types of memory as the I/O unit buffer. The allowed
values are:
Use memory from :manpage:`malloc(3)` as the buffers. Default memory
Use shared memory as the buffers. Allocated through
Same as shm, but use huge pages as backing.
Use mmap to allocate buffers. May either be anonymous memory, or can
be file backed if a filename is given after the option. The format
is `mem=mmap:/path/to/file`.
Use a memory mapped huge file as the buffer backing. Append filename
after mmaphuge, ala `mem=mmaphuge:/hugetlbfs/file`.
Same as mmap, but use a MMAP_SHARED mapping.
Use GPU memory as the buffers for GPUDirect RDMA benchmark.
The area allocated is a function of the maximum allowed bs size for the job,
multiplied by the I/O depth given. Note that for **shmhuge** and
**mmaphuge** to work, the system must have free huge pages allocated. This
can normally be checked and set by reading/writing
:file:`/proc/sys/vm/nr_hugepages` on a Linux system. Fio assumes a huge page
is 4MiB in size. So to calculate the number of huge pages you need for a
given job file, add up the I/O depth of all jobs (normally one unless
:option:`iodepth` is used) and multiply by the maximum bs set. Then divide
that number by the huge page size. You can see the size of the huge pages in
:file:`/proc/meminfo`. If no huge pages are allocated by having a non-zero
number in `nr_hugepages`, using **mmaphuge** or **shmhuge** will fail. Also
see :option:`hugepage-size`.
**mmaphuge** also needs to have hugetlbfs mounted and the file location
should point there. So if it's mounted in :file:`/huge`, you would use
.. option:: iomem_align=int
This indicates the memory alignment of the I/O memory buffers. Note that
the given alignment is applied to the first I/O unit buffer, if using
:option:`iodepth` the alignment of the following buffers are given by the
:option:`bs` used. In other words, if using a :option:`bs` that is a
multiple of the page sized in the system, all buffers will be aligned to
this value. If using a :option:`bs` that is not page aligned, the alignment
of subsequent I/O memory buffers is the sum of the :option:`iomem_align` and
:option:`bs` used.
.. option:: hugepage-size=int
Defines the size of a huge page. Must at least be equal to the system
setting, see :file:`/proc/meminfo`. Defaults to 4MiB. Should probably
always be a multiple of megabytes, so using ``hugepage-size=Xm`` is the
preferred way to set this to avoid setting a non-pow-2 bad value.
.. option:: lockmem=int
Pin the specified amount of memory with :manpage:`mlock(2)`. Can be used to
simulate a smaller amount of memory. The amount specified is per worker.
I/O size
.. option:: size=int
The total size of file I/O for each thread of this job. Fio will run until
this many bytes has been transferred, unless runtime is limited by other options
(such as :option:`runtime`, for instance, or increased/decreased by :option:`io_size`).
Fio will divide this size between the available files determined by options
such as :option:`nrfiles`, :option:`filename`, unless :option:`filesize` is
specified by the job. If the result of division happens to be 0, the size is
set to the physical size of the given files or devices if they exist.
If this option is not specified, fio will use the full size of the given
files or devices. If the files do not exist, size must be given. It is also
possible to give size as a percentage between 1 and 100. If ``size=20%`` is
given, fio will use 20% of the full size of the given files or devices.
Can be combined with :option:`offset` to constrain the start and end range
that I/O will be done within.
.. option:: io_size=int, io_limit=int
Normally fio operates within the region set by :option:`size`, which means
that the :option:`size` option sets both the region and size of I/O to be
performed. Sometimes that is not what you want. With this option, it is
possible to define just the amount of I/O that fio should do. For instance,
if :option:`size` is set to 20GiB and :option:`io_size` is set to 5GiB, fio
will perform I/O within the first 20GiB but exit when 5GiB have been
done. The opposite is also possible -- if :option:`size` is set to 20GiB,
and :option:`io_size` is set to 40GiB, then fio will do 40GiB of I/O within
the 0..20GiB region.
.. option:: filesize=int
Individual file sizes. May be a range, in which case fio will select sizes
for files at random within the given range and limited to :option:`size` in
total (if that is given). If not given, each created file is the same size.
This option overrides :option:`size` in terms of file size, which means
this value is used as a fixed size or possible range of each file.
.. option:: file_append=bool
Perform I/O after the end of the file. Normally fio will operate within the
size of a file. If this option is set, then fio will append to the file
instead. This has identical behavior to setting :option:`offset` to the size
of a file. This option is ignored on non-regular files.
.. option:: fill_device=bool, fill_fs=bool
Sets size to something really large and waits for ENOSPC (no space left on
device) as the terminating condition. Only makes sense with sequential
write. For a read workload, the mount point will be filled first then I/O
started on the result. This option doesn't make sense if operating on a raw
device node, since the size of that is already known by the file system.
Additionally, writing beyond end-of-device will not return ENOSPC there.
I/O engine
.. option:: ioengine=str
Defines how the job issues I/O to the file. The following types are defined:
Basic :manpage:`read(2)` or :manpage:`write(2)`
I/O. :manpage:`lseek(2)` is used to position the I/O location.
See :option:`fsync` and :option:`fdatasync` for syncing write I/Os.
Basic :manpage:`pread(2)` or :manpage:`pwrite(2)` I/O. Default on
all supported operating systems except for Windows.
Basic :manpage:`readv(2)` or :manpage:`writev(2)` I/O. Will emulate
queuing by coalescing adjacent I/Os into a single submission.
Basic :manpage:`preadv(2)` or :manpage:`pwritev(2)` I/O.
Basic :manpage:`preadv2(2)` or :manpage:`pwritev2(2)` I/O.
Linux native asynchronous I/O. Note that Linux may only support
queued behaviour with non-buffered I/O (set ``direct=1`` or
This engine defines engine specific options.
POSIX asynchronous I/O using :manpage:`aio_read(3)` and
Solaris native asynchronous I/O.
Windows native asynchronous I/O. Default on Windows.
File is memory mapped with :manpage:`mmap(2)` and data copied
to/from using :manpage:`memcpy(3)`.
:manpage:`splice(2)` is used to transfer the data and
:manpage:`vmsplice(2)` to transfer data from user space to the
SCSI generic sg v3 I/O. May either be synchronous using the SG_IO
ioctl, or if the target is an sg character device we use
:manpage:`read(2)` and :manpage:`write(2)` for asynchronous
I/O. Requires filename option to specify either block or character
Doesn't transfer any data, just pretends to. This is mainly used to
exercise fio itself and for debugging/testing purposes.
Transfer over the network to given ``host:port``. Depending on the
:option:`protocol` used, the :option:`hostname`, :option:`port`,
:option:`listen` and :option:`filename` options are used to specify
what sort of connection to make, while the :option:`protocol` option
determines which protocol will be used. This engine defines engine
specific options.
Like **net**, but uses :manpage:`splice(2)` and
:manpage:`vmsplice(2)` to map data and send/receive.
This engine defines engine specific options.
Doesn't transfer any data, but burns CPU cycles according to the
:option:`cpuload` and :option:`cpuchunks` options. Setting
:option:`cpuload` =85 will cause that job to do nothing but burn 85%
of the CPU. In case of SMP machines, use :option:`numjobs`
=<no_of_cpu> to get desired CPU usage, as the cpuload only loads a
single CPU at the desired rate. A job never finishes unless there is
at least one non-cpuio job.
The GUASI I/O engine is the Generic Userspace Asyncronous Syscall
Interface approach to async I/O. See
for more info on GUASI.
The RDMA I/O engine supports both RDMA memory semantics
(RDMA_WRITE/RDMA_READ) and channel semantics (Send/Recv) for the
InfiniBand, RoCE and iWARP protocols.
I/O engine that does regular fallocate to simulate data transfer as
fio ioengine.
does fallocate(,mode = FALLOC_FL_KEEP_SIZE,).
does fallocate(,mode = 0).
I/O engine that sends :manpage:`ftruncate(2)` operations in response
to write (DDIR_WRITE) events. Each ftruncate issued sets the file's
size to the current block offset. Block size is ignored.
I/O engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate
defragment activity in request to DDIR_WRITE event.
I/O engine supporting direct access to Ceph Rados Block Devices
(RBD) via librbd without the need to use the kernel rbd driver. This
ioengine defines engine specific options.
Using Glusterfs libgfapi sync interface to direct access to
Glusterfs volumes without having to go through FUSE. This ioengine
defines engine specific options.
Using Glusterfs libgfapi async interface to direct access to
Glusterfs volumes without having to go through FUSE. This ioengine
defines engine specific options.
Read and write through Hadoop (HDFS). The :file:`filename` option
is used to specify host,port of the hdfs name-node to connect. This
engine interprets offsets a little differently. In HDFS, files once
created cannot be modified. So random writes are not possible. To
imitate this, libhdfs engine expects bunch of small files to be
created over HDFS, and engine will randomly pick a file out of those
files based on the offset generated by fio backend. (see the example
job file to create such files, use ``rw=write`` option). Please
note, you might want to set necessary environment variables to work
with hdfs/libhdfs properly. Each job uses its own connection to
Read, write and erase an MTD character device (e.g.,
:file:`/dev/mtd0`). Discards are treated as erases. Depending on the
underlying device type, the I/O may have to go in a certain pattern,
e.g., on NAND, writing sequentially to erase blocks and discarding
before overwriting. The writetrim mode works well for this
Read and write using filesystem DAX to a file on a filesystem
mounted with DAX on a persistent memory device through the NVML
libpmemblk library.
Read and write using device DAX to a persistent memory device (e.g.,
/dev/dax0.0) through the NVML libpmem library.
Prefix to specify loading an external I/O engine object file. Append
the engine filename, e.g. ``ioengine=external:/tmp/foo.o`` to load
ioengine :file:`foo.o` in :file:`/tmp`.
I/O engine specific parameters
In addition, there are some parameters which are only valid when a specific
ioengine is in use. These are used identically to normal parameters, with the
caveat that when used on the command line, they must come after the
:option:`ioengine` that defines them is selected.
.. option:: userspace_reap : [libaio]
Normally, with the libaio engine in use, fio will use the
:manpage:`io_getevents(2)` system call to reap newly returned events. With
this flag turned on, the AIO ring will be read directly from user-space to
reap events. The reaping mode is only enabled when polling for a minimum of
0 events (e.g. when :option:`iodepth_batch_complete` `=0`).
.. option:: hipri : [pvsync2]
Set RWF_HIPRI on I/O, indicating to the kernel that it's of higher priority
than normal.
.. option:: cpuload=int : [cpuio]
Attempt to use the specified percentage of CPU cycles. This is a mandatory
option when using cpuio I/O engine.
.. option:: cpuchunks=int : [cpuio]
Split the load into cycles of the given time. In microseconds.
.. option:: exit_on_io_done=bool : [cpuio]
Detect when I/O threads are done, then exit.
.. option:: hostname=str : [netsplice] [net]
The host name or IP address to use for TCP or UDP based I/O. If the job is
a TCP listener or UDP reader, the host name is not used and must be omitted
unless it is a valid UDP multicast address.
.. option:: namenode=str : [libhdfs]
The host name or IP address of a HDFS cluster namenode to contact.
.. option:: port=int
[netsplice], [net]
The TCP or UDP port to bind to or connect to. If this is used with
:option:`numjobs` to spawn multiple instances of the same job type, then
this will be the starting port number since fio will use a range of
the listening port of the HFDS cluster namenode.
.. option:: interface=str : [netsplice] [net]
The IP address of the network interface used to send or receive UDP
.. option:: ttl=int : [netsplice] [net]
Time-to-live value for outgoing UDP multicast packets. Default: 1.
.. option:: nodelay=bool : [netsplice] [net]
Set TCP_NODELAY on TCP connections.
.. option:: protocol=str : [netsplice] [net]
.. option:: proto=str : [netsplice] [net]
The network protocol to use. Accepted values are:
Transmission control protocol.
Transmission control protocol V6.
User datagram protocol.
User datagram protocol V6.
UNIX domain socket.
When the protocol is TCP or UDP, the port must also be given, as well as the
hostname if the job is a TCP listener or UDP reader. For unix sockets, the
normal filename option should be used and the port is invalid.
.. option:: listen : [net]
For TCP network connections, tell fio to listen for incoming connections
rather than initiating an outgoing connection. The :option:`hostname` must
be omitted if this option is used.
.. option:: pingpong : [net]
Normally a network writer will just continue writing data, and a network
reader will just consume packages. If ``pingpong=1`` is set, a writer will
send its normal payload to the reader, then wait for the reader to send the
same payload back. This allows fio to measure network latencies. The
submission and completion latencies then measure local time spent sending or
receiving, and the completion latency measures how long it took for the
other end to receive and send back. For UDP multicast traffic
``pingpong=1`` should only be set for a single reader when multiple readers
are listening to the same address.
.. option:: window_size : [net]
Set the desired socket buffer size for the connection.
.. option:: mss : [net]
Set the TCP maximum segment size (TCP_MAXSEG).
.. option:: donorname=str : [e4defrag]
File will be used as a block donor(swap extents between files).
.. option:: inplace=int : [e4defrag]
Configure donor file blocks allocation strategy:
Default. Preallocate donor's file on init.
Allocate space immediately inside defragment event, and free right
after event.
.. option:: clustername=str : [rbd]
Specifies the name of the Ceph cluster.
.. option:: rbdname=str : [rbd]
Specifies the name of the RBD.
.. option:: pool=str : [rbd]
Specifies the name of the Ceph pool containing RBD.
.. option:: clientname=str : [rbd]
Specifies the username (without the 'client.' prefix) used to access the
Ceph cluster. If the *clustername* is specified, the *clientname* shall be
the full ** string. If no type. prefix is given, fio will add
'client.' by default.
.. option:: skip_bad=bool : [mtd]
Skip operations against known bad blocks.
.. option:: hdfsdirectory : [libhdfs]
libhdfs will create chunk in this HDFS directory.
.. option:: chunk_size : [libhdfs]
the size of the chunk to use for each file.
I/O depth
.. option:: iodepth=int
Number of I/O units to keep in flight against the file. Note that
increasing *iodepth* beyond 1 will not affect synchronous ioengines (except
for small degrees when :option:`verify_async` is in use). Even async
engines may impose OS restrictions causing the desired depth not to be
achieved. This may happen on Linux when using libaio and not setting
:option:`direct` =1, since buffered I/O is not async on that OS. Keep an
eye on the I/O depth distribution in the fio output to verify that the
achieved depth is as expected. Default: 1.
.. option:: iodepth_batch_submit=int, iodepth_batch=int
This defines how many pieces of I/O to submit at once. It defaults to 1
which means that we submit each I/O as soon as it is available, but can be
raised to submit bigger batches of I/O at the time. If it is set to 0 the
:option:`iodepth` value will be used.
.. option:: iodepth_batch_complete_min=int, iodepth_batch_complete=int
This defines how many pieces of I/O to retrieve at once. It defaults to 1
which means that we'll ask for a minimum of 1 I/O in the retrieval process
from the kernel. The I/O retrieval will go on until we hit the limit set by
:option:`iodepth_low`. If this variable is set to 0, then fio will always
check for completed events before queuing more I/O. This helps reduce I/O
latency, at the cost of more retrieval system calls.
.. option:: iodepth_batch_complete_max=int
This defines maximum pieces of I/O to retrieve at once. This variable should
be used along with :option:`iodepth_batch_complete_min` =int variable,
specifying the range of min and max amount of I/O which should be
retrieved. By default it is equal to :option:`iodepth_batch_complete_min`
Example #1::
which means that we will retrieve at least 1 I/O and up to the whole
submitted queue depth. If none of I/O has been completed yet, we will wait.
Example #2::
which means that we can retrieve up to the whole submitted queue depth, but
if none of I/O has been completed yet, we will NOT wait and immediately exit
the system call. In this example we simply do polling.
.. option:: iodepth_low=int
The low water mark indicating when to start filling the queue
again. Defaults to the same as :option:`iodepth`, meaning that fio will
attempt to keep the queue full at all times. If :option:`iodepth` is set to
e.g. 16 and *iodepth_low* is set to 4, then after fio has filled the queue of
16 requests, it will let the depth drain down to 4 before starting to fill
it again.
.. option:: io_submit_mode=str
This option controls how fio submits the I/O to the I/O engine. The default
is `inline`, which means that the fio job threads submit and reap I/O
directly. If set to `offload`, the job threads will offload I/O submission
to a dedicated pool of I/O threads. This requires some coordination and thus
has a bit of extra overhead, especially for lower queue depth I/O where it
can increase latencies. The benefit is that fio can manage submission rates
independently of the device completion rates. This avoids skewed latency
reporting if I/O gets back up on the device side (the coordinated omission
I/O rate
.. option:: thinktime=time
Stall the job for the specified period of time after an I/O has completed before issuing the
next. May be used to simulate processing being done by an application.
When the unit is omitted, the value is given in microseconds. See
:option:`thinktime_blocks` and :option:`thinktime_spin`.
.. option:: thinktime_spin=time
Only valid if :option:`thinktime` is set - pretend to spend CPU time doing
something with the data received, before falling back to sleeping for the
rest of the period specified by :option:`thinktime`. When the unit is
omitted, the value is given in microseconds.
.. option:: thinktime_blocks=int
Only valid if :option:`thinktime` is set - control how many blocks to issue,
before waiting `thinktime` usecs. If not set, defaults to 1 which will make
fio wait `thinktime` usecs after every block. This effectively makes any
queue depth setting redundant, since no more than 1 I/O will be queued
before we have to complete it and do our thinktime. In other words, this
setting effectively caps the queue depth if the latter is larger.
.. option:: rate=int[,int][,int]
Cap the bandwidth used by this job. The number is in bytes/sec, the normal
suffix rules apply. Comma-separated values may be specified for reads,
writes, and trims as described in :option:`blocksize`.
.. option:: rate_min=int[,int][,int]
Tell fio to do whatever it can to maintain at least this bandwidth. Failing
to meet this requirement will cause the job to exit. Comma-separated values
may be specified for reads, writes, and trims as described in
.. option:: rate_iops=int[,int][,int]
Cap the bandwidth to this number of IOPS. Basically the same as
:option:`rate`, just specified independently of bandwidth. If the job is
given a block size range instead of a fixed value, the smallest block size
is used as the metric. Comma-separated values may be specified for reads,
writes, and trims as described in :option:`blocksize`.
.. option:: rate_iops_min=int[,int][,int]
If fio doesn't meet this rate of I/O, it will cause the job to exit.
Comma-separated values may be specified for reads, writes, and trims as
described in :option:`blocksize`.
.. option:: rate_process=str
This option controls how fio manages rated I/O submissions. The default is
`linear`, which submits I/O in a linear fashion with fixed delays between
I/Os that gets adjusted based on I/O completion rates. If this is set to
`poisson`, fio will submit I/O based on a more real world random request
flow, known as the Poisson process
( The lambda will be
10^6 / IOPS for the given workload.
I/O latency
.. option:: latency_target=time
If set, fio will attempt to find the max performance point that the given
workload will run at while maintaining a latency below this target. When
the unit is omitted, the value is given in microseconds. See
:option:`latency_window` and :option:`latency_percentile`.
.. option:: latency_window=time
Used with :option:`latency_target` to specify the sample window that the job
is run at varying queue depths to test the performance. When the unit is
omitted, the value is given in microseconds.
.. option:: latency_percentile=float
The percentage of I/Os that must fall within the criteria specified by
:option:`latency_target` and :option:`latency_window`. If not set, this
defaults to 100.0, meaning that all I/Os must be equal or below to the value
set by :option:`latency_target`.
.. option:: max_latency=time
If set, fio will exit the job with an ETIMEDOUT error if it exceeds this
maximum latency. When the unit is omitted, the value is given in
.. option:: rate_cycle=int
Average bandwidth for :option:`rate` and :option:`rate_min` over this number
of milliseconds.
I/O replay
.. option:: write_iolog=str
Write the issued I/O patterns to the specified file. See
:option:`read_iolog`. Specify a separate file for each job, otherwise the
iologs will be interspersed and the file may be corrupt.
.. option:: read_iolog=str
Open an iolog with the specified file name and replay the I/O patterns it
contains. This can be used to store a workload and replay it sometime
later. The iolog given may also be a blktrace binary file, which allows fio
to replay a workload captured by :command:`blktrace`. See
:manpage:`blktrace(8)` for how to capture such logging data. For blktrace
replay, the file needs to be turned into a blkparse binary data file first
(``blkparse <device> -o /dev/null -d file_for_fio.bin``).
.. option:: replay_no_stall=int
When replaying I/O with :option:`read_iolog` the default behavior is to
attempt to respect the time stamps within the log and replay them with the
appropriate delay between IOPS. By setting this variable fio will not
respect the timestamps and attempt to replay them as fast as possible while
still respecting ordering. The result is the same I/O pattern to a given
device, but different timings.
.. option:: replay_redirect=str
While replaying I/O patterns using :option:`read_iolog` the default behavior
is to replay the IOPS onto the major/minor device that each IOP was recorded
from. This is sometimes undesirable because on a different machine those
major/minor numbers can map to a different device. Changing hardware on the
same system can also result in a different major/minor mapping.
``replay_redirect`` causes all IOPS to be replayed onto the single specified
device regardless of the device it was recorded
from. i.e. :option:`replay_redirect` = :file:`/dev/sdc` would cause all I/O
in the blktrace or iolog to be replayed onto :file:`/dev/sdc`. This means
multiple devices will be replayed onto a single device, if the trace
contains multiple devices. If you want multiple devices to be replayed
concurrently to multiple redirected devices you must blkparse your trace
into separate traces and replay them with independent fio invocations.
Unfortunately this also breaks the strict time ordering between multiple
device accesses.
.. option:: replay_align=int
Force alignment of I/O offsets and lengths in a trace to this power of 2
.. option:: replay_scale=int
Scale sector offsets down by this factor when replaying traces.
Threads, processes and job synchronization
.. option:: thread
Fio defaults to forking jobs, however if this option is given, fio will use
POSIX Threads function :manpage:`pthread_create(3)` to create threads instead
of forking processes.
.. option:: wait_for=str
Specifies the name of the already defined job to wait for. Single waitee
name only may be specified. If set, the job won't be started until all
workers of the waitee job are done.
``wait_for`` operates on the job name basis, so there are a few
limitations. First, the waitee must be defined prior to the waiter job
(meaning no forward references). Second, if a job is being referenced as a
waitee, it must have a unique name (no duplicate waitees).
.. option:: nice=int
Run the job with the given nice value. See man :manpage:`nice(2)`.
On Windows, values less than -15 set the process class to "High"; -1 through
-15 set "Above Normal"; 1 through 15 "Below Normal"; and above 15 "Idle"
priority class.
.. option:: prio=int
Set the I/O priority value of this job. Linux limits us to a positive value
between 0 and 7, with 0 being the highest. See man
:manpage:`ionice(1)`. Refer to an appropriate manpage for other operating
systems since meaning of priority may differ.
.. option:: prioclass=int
Set the I/O priority class. See man :manpage:`ionice(1)`.
.. option:: cpumask=int
Set the CPU affinity of this job. The parameter given is a bitmask of
allowed CPU's the job may run on. So if you want the allowed CPUs to be 1
and 5, you would pass the decimal value of (1 << 1 | 1 << 5), or 34. See man
:manpage:`sched_setaffinity(2)`. This may not work on all supported
operating systems or kernel versions. This option doesn't work well for a
higher CPU count than what you can store in an integer mask, so it can only
control cpus 1-32. For boxes with larger CPU counts, use
.. option:: cpus_allowed=str
Controls the same options as :option:`cpumask`, but it allows a text setting
of the permitted CPUs instead. So to use CPUs 1 and 5, you would specify
``cpus_allowed=1,5``. This options also allows a range of CPUs. Say you
wanted a binding to CPUs 1, 5, and 8-15, you would set
.. option:: cpus_allowed_policy=str
Set the policy of how fio distributes the CPUs specified by
:option:`cpus_allowed` or cpumask. Two policies are supported:
All jobs will share the CPU set specified.
Each job will get a unique CPU from the CPU set.
**shared** is the default behaviour, if the option isn't specified. If
**split** is specified, then fio will will assign one cpu per job. If not
enough CPUs are given for the jobs listed, then fio will roundrobin the CPUs
in the set.
.. option:: numa_cpu_nodes=str
Set this job running on specified NUMA nodes' CPUs. The arguments allow
comma delimited list of cpu numbers, A-B ranges, or `all`. Note, to enable
numa options support, fio must be built on a system with libnuma-dev(el)
.. option:: numa_mem_policy=str
Set this job's memory policy and corresponding NUMA nodes. Format of the
``mode`` is one of the following memory policy: ``default``, ``prefer``,
``bind``, ``interleave``, ``local`` For ``default`` and ``local`` memory
policy, no node is needed to be specified. For ``prefer``, only one node is
allowed. For ``bind`` and ``interleave``, it allow comma delimited list of
numbers, A-B ranges, or `all`.
.. option:: cgroup=str
Add job to this control group. If it doesn't exist, it will be created. The
system must have a mounted cgroup blkio mount point for this to work. If
your system doesn't have it mounted, you can do so with::
# mount -t cgroup -o blkio none /cgroup
.. option:: cgroup_weight=int
Set the weight of the cgroup to this value. See the documentation that comes
with the kernel, allowed values are in the range of 100..1000.
.. option:: cgroup_nodelete=bool
Normally fio will delete the cgroups it has created after the job
completion. To override this behavior and to leave cgroups around after the
job completion, set ``cgroup_nodelete=1``. This can be useful if one wants
to inspect various cgroup files after job completion. Default: false.
.. option:: flow_id=int
The ID of the flow. If not specified, it defaults to being a global
flow. See :option:`flow`.
.. option:: flow=int
Weight in token-based flow control. If this value is used, then there is a
'flow counter' which is used to regulate the proportion of activity between
two or more jobs. Fio attempts to keep this flow counter near zero. The
``flow`` parameter stands for how much should be added or subtracted to the
flow counter on each iteration of the main I/O loop. That is, if one job has
``flow=8`` and another job has ``flow=-1``, then there will be a roughly 1:8
ratio in how much one runs vs the other.
.. option:: flow_watermark=int
The maximum value that the absolute value of the flow counter is allowed to
reach before the job must wait for a lower value of the counter.
.. option:: flow_sleep=int
The period of time, in microseconds, to wait after the flow watermark has
been exceeded before retrying operations.
.. option:: stonewall, wait_for_previous
Wait for preceding jobs in the job file to exit, before starting this
one. Can be used to insert serialization points in the job file. A stone
wall also implies starting a new reporting group, see
.. option:: exitall
When one job finishes, terminate the rest. The default is to wait for each
job to finish, sometimes that is not the desired action.
.. option:: exec_prerun=str
Before running this job, issue the command specified through
:manpage:`system(3)`. Output is redirected in a file called
.. option:: exec_postrun=str
After the job completes, issue the command specified though
:manpage:`system(3)`. Output is redirected in a file called
.. option:: uid=int
Instead of running as the invoking user, set the user ID to this value
before the thread/process does any work.
.. option:: gid=int
Set group ID, see :option:`uid`.
.. option:: verify_only
Do not perform specified workload, only verify data still matches previous
invocation of this workload. This option allows one to check data multiple
times at a later date without overwriting it. This option makes sense only
for workloads that write data, and does not support workloads with the
:option:`time_based` option set.
.. option:: do_verify=bool
Run the verify phase after a write phase. Only valid if :option:`verify` is
set. Default: true.
.. option:: verify=str
If writing to a file, fio can verify the file contents after each iteration
of the job. Each verification method also implies verification of special
header, which is written to the beginning of each block. This header also
includes meta information, like offset of the block, block number, timestamp
when block was written, etc. :option:`verify` can be combined with
:option:`verify_pattern` option. The allowed values are:
Use an md5 sum of the data area and store it in the header of
each block.
Use an experimental crc64 sum of the data area and store it in the
header of each block.
Use a crc32c sum of the data area and store it in the header of each
Use hardware assisted crc32c calculation provided on SSE4.2 enabled
processors. Falls back to regular software crc32c, if not supported
by the system.
Use a crc32 sum of the data area and store it in the header of each
Use a crc16 sum of the data area and store it in the header of each
Use a crc7 sum of the data area and store it in the header of each
Use xxhash as the checksum function. Generally the fastest software
checksum that fio supports.
Use sha512 as the checksum function.
Use sha256 as the checksum function.
Use optimized sha1 as the checksum function.
Use optimized sha3-224 as the checksum function.
Use optimized sha3-256 as the checksum function.
Use optimized sha3-384 as the checksum function.
Use optimized sha3-512 as the checksum function.
This option is deprecated, since now meta information is included in
generic verification header and meta verification happens by
default. For detailed information see the description of the
:option:`verify` setting. This option is kept because of
compatibility's sake with old configurations. Do not use it.
Verify a strict pattern. Normally fio includes a header with some
basic information and checksumming, but if this option is set, only
the specific pattern set with :option:`verify_pattern` is verified.
Only pretend to verify. Useful for testing internals with
:option:`ioengine` `=null`, not for much else.
This option can be used for repeated burn-in tests of a system to make sure
that the written data is also correctly read back. If the data direction
given is a read or random read, fio will assume that it should verify a
previously written file. If the data direction includes any form of write,
the verify will be of the newly written data.
.. option:: verifysort=bool
If true, fio will sort written verify blocks when it deems it faster to read
them back in a sorted manner. This is often the case when overwriting an
existing file, since the blocks are already laid out in the file system. You
can ignore this option unless doing huge amounts of really fast I/O where
the red-black tree sorting CPU time becomes significant. Default: true.
.. option:: verifysort_nr=int
Pre-load and sort verify blocks for a read workload.
.. option:: verify_offset=int
Swap the verification header with data somewhere else in the block before
writing. It is swapped back before verifying.
.. option:: verify_interval=int
Write the verification header at a finer granularity than the
:option:`blocksize`. It will be written for chunks the size of
``verify_interval``. :option:`blocksize` should divide this evenly.
.. option:: verify_pattern=str
If set, fio will fill the I/O buffers with this pattern. Fio defaults to
filling with totally random bytes, but sometimes it's interesting to fill
with a known pattern for I/O verification purposes. Depending on the width
of the pattern, fio will fill 1/2/3/4 bytes of the buffer at the time(it can
be either a decimal or a hex number). The ``verify_pattern`` if larger than
a 32-bit quantity has to be a hex number that starts with either "0x" or
"0X". Use with :option:`verify`. Also, ``verify_pattern`` supports %o
format, which means that for each block offset will be written and then
verified back, e.g.::
Or use combination of everything::
.. option:: verify_fatal=bool
Normally fio will keep checking the entire contents before quitting on a
block verification failure. If this option is set, fio will exit the job on
the first observed failure. Default: false.
.. option:: verify_dump=bool
If set, dump the contents of both the original data block and the data block
we read off disk to files. This allows later analysis to inspect just what
kind of data corruption occurred. Off by default.
.. option:: verify_async=int
Fio will normally verify I/O inline from the submitting thread. This option
takes an integer describing how many async offload threads to create for I/O
verification instead, causing fio to offload the duty of verifying I/O
contents to one or more separate threads. If using this offload option, even
sync I/O engines can benefit from using an :option:`iodepth` setting higher
than 1, as it allows them to have I/O in flight while verifies are running.
.. option:: verify_async_cpus=str
Tell fio to set the given CPU affinity on the async I/O verification
threads. See :option:`cpus_allowed` for the format used.
.. option:: verify_backlog=int
Fio will normally verify the written contents of a job that utilizes verify
once that job has completed. In other words, everything is written then
everything is read back and verified. You may want to verify continually
instead for a variety of reasons. Fio stores the meta data associated with
an I/O block in memory, so for large verify workloads, quite a bit of memory
would be used up holding this meta data. If this option is enabled, fio will
write only N blocks before verifying these blocks.
.. option:: verify_backlog_batch=int
Control how many blocks fio will verify if :option:`verify_backlog` is
set. If not set, will default to the value of :option:`verify_backlog`
(meaning the entire queue is read back and verified). If
``verify_backlog_batch`` is less than :option:`verify_backlog` then not all
blocks will be verified, if ``verify_backlog_batch`` is larger than
:option:`verify_backlog`, some blocks will be verified more than once.
.. option:: verify_state_save=bool
When a job exits during the write phase of a verify workload, save its
current state. This allows fio to replay up until that point, if the verify
state is loaded for the verify read phase. The format of the filename is,
<type> is "local" for a local run, "sock" for a client/server socket
connection, and "ip" (, for instance) for a networked
client/server connection.
.. option:: verify_state_load=bool
If a verify termination trigger was used, fio stores the current write state
of each thread. This can be used at verification time so that fio knows how
far it should verify. Without this information, fio will run a full
verification pass, according to the settings in the job file used.
.. option:: trim_percentage=int
Number of verify blocks to discard/trim.
.. option:: trim_verify_zero=bool
Verify that trim/discarded blocks are returned as zeroes.
.. option:: trim_backlog=int
Verify that trim/discarded blocks are returned as zeroes.
.. option:: trim_backlog_batch=int
Trim this number of I/O blocks.
.. option:: experimental_verify=bool
Enable experimental verification.
Steady state
.. option:: steadystate=str:float, ss=str:float
Define the criterion and limit for assessing steady state performance. The
first parameter designates the criterion whereas the second parameter sets
the threshold. When the criterion falls below the threshold for the
specified duration, the job will stop. For example, `iops_slope:0.1%` will
direct fio to terminate the job when the least squares regression slope
falls below 0.1% of the mean IOPS. If :option:`group_reporting` is enabled
this will apply to all jobs in the group. Below is the list of available
steady state assessment criteria. All assessments are carried out using only
data from the rolling collection window. Threshold limits can be expressed
as a fixed value or as a percentage of the mean in the collection window.
Collect IOPS data. Stop the job if all individual IOPS measurements
are within the specified limit of the mean IOPS (e.g., ``iops:2``
means that all individual IOPS values must be within 2 of the mean,
whereas ``iops:0.2%`` means that all individual IOPS values must be
within 0.2% of the mean IOPS to terminate the job).
Collect IOPS data and calculate the least squares regression
slope. Stop the job if the slope falls below the specified limit.
Collect bandwidth data. Stop the job if all individual bandwidth
measurements are within the specified limit of the mean bandwidth.
Collect bandwidth data and calculate the least squares regression
slope. Stop the job if the slope falls below the specified limit.
.. option:: steadystate_duration=time, ss_dur=time
A rolling window of this duration will be used to judge whether steady state
has been reached. Data will be collected once per second. The default is 0
which disables steady state detection. When the unit is omitted, the
value is given in seconds.
.. option:: steadystate_ramp_time=time, ss_ramp=time
Allow the job to run for the specified duration before beginning data
collection for checking the steady state job termination criterion. The
default is 0. When the unit is omitted, the value is given in seconds.
Measurements and reporting
.. option:: per_job_logs=bool
If set, this generates bw/clat/iops log with per file private filenames. If
not set, jobs with identical names will share the log filename. Default:
.. option:: group_reporting
It may sometimes be interesting to display statistics for groups of jobs as
a whole instead of for each individual job. This is especially true if
:option:`numjobs` is used; looking at individual thread/process output
quickly becomes unwieldy. To see the final report per-group instead of
per-job, use :option:`group_reporting`. Jobs in a file will be part of the
same reporting group, unless if separated by a :option:`stonewall`, or by
using :option:`new_group`.
.. option:: new_group
Start a new reporting group. See: :option:`group_reporting`. If not given,
all jobs in a file will be part of the same reporting group, unless
separated by a :option:`stonewall`.
.. option:: stats
By default, fio collects and shows final output results for all jobs
that run. If this option is set to 0, then fio will ignore it in
the final stat output.
.. option:: write_bw_log=str
If given, write a bandwidth log for this job. Can be used to store data of
the bandwidth of the jobs in their lifetime. The included
:command:`fio_generate_plots` script uses :command:`gnuplot` to turn these
text files into nice graphs. See :option:`write_lat_log` for behaviour of
given filename. For this option, the postfix is :file:`_bw.x.log`, where `x`
is the index of the job (`1..N`, where `N` is the number of jobs). If
:option:`per_job_logs` is false, then the filename will not include the job
index. See `Log File Formats`_.
.. option:: write_lat_log=str
Same as :option:`write_bw_log`, except that this option stores I/O
submission, completion, and total latencies instead. If no filename is given
with this option, the default filename of :file:`jobname_type.log` is
used. Even if the filename is given, fio will still append the type of
log. So if one specifies::
The actual log names will be :file:`foo_slat.x.log`, :file:`foo_clat.x.log`,
and :file:`foo_lat.x.log`, where `x` is the index of the job (1..N, where N
is the number of jobs). This helps :command:`fio_generate_plot` find the
logs automatically. If :option:`per_job_logs` is false, then the filename
will not include the job index. See `Log File Formats`_.
.. option:: write_hist_log=str
Same as :option:`write_lat_log`, but writes I/O completion latency
histograms. If no filename is given with this option, the default filename
of :file:`jobname_clat_hist.x.log` is used, where `x` is the index of the
job (1..N, where `N` is the number of jobs). Even if the filename is given,
fio will still append the type of log. If :option:`per_job_logs` is false,
then the filename will not include the job index. See `Log File Formats`_.
.. option:: write_iops_log=str
Same as :option:`write_bw_log`, but writes IOPS. If no filename is given
with this option, the default filename of :file:`jobname_type.x.log` is
used,where `x` is the index of the job (1..N, where `N` is the number of
jobs). Even if the filename is given, fio will still append the type of
log. If :option:`per_job_logs` is false, then the filename will not include
the job index. See `Log File Formats`_.
.. option:: log_avg_msec=int
By default, fio will log an entry in the iops, latency, or bw log for every
I/O that completes. When writing to the disk log, that can quickly grow to a
very large size. Setting this option makes fio average the each log entry
over the specified period of time, reducing the resolution of the log. See
:option:`log_max_value` as well. Defaults to 0, logging all entries.
.. option:: log_hist_msec=int
Same as :option:`log_avg_msec`, but logs entries for completion latency
histograms. Computing latency percentiles from averages of intervals using
:option:`log_avg_msec` is inaccurate. Setting this option makes fio log
histogram entries over the specified period of time, reducing log sizes for
high IOPS devices while retaining percentile accuracy. See
:option:`log_hist_coarseness` as well. Defaults to 0, meaning histogram
logging is disabled.
.. option:: log_hist_coarseness=int
Integer ranging from 0 to 6, defining the coarseness of the resolution of
the histogram logs enabled with :option:`log_hist_msec`. For each increment
in coarseness, fio outputs half as many bins. Defaults to 0, for which
histogram logs contain 1216 latency bins. See `Log File Formats`_.
.. option:: log_max_value=bool
If :option:`log_avg_msec` is set, fio logs the average over that window. If
you instead want to log the maximum value, set this option to 1. Defaults to
0, meaning that averaged values are logged.
.. option:: log_offset=int
If this is set, the iolog options will include the byte offset for the I/O
entry as well as the other data values.
.. option:: log_compression=int
If this is set, fio will compress the I/O logs as it goes, to keep the
memory footprint lower. When a log reaches the specified size, that chunk is
removed and compressed in the background. Given that I/O logs are fairly
highly compressible, this yields a nice memory savings for longer runs. The
downside is that the compression will consume some background CPU cycles, so
it may impact the run. This, however, is also true if the logging ends up
consuming most of the system memory. So pick your poison. The I/O logs are
saved normally at the end of a run, by decompressing the chunks and storing
them in the specified log file. This feature depends on the availability of
.. option:: log_compression_cpus=str
Define the set of CPUs that are allowed to handle online log compression for
the I/O jobs. This can provide better isolation between performance
sensitive jobs, and background compression work.
.. option:: log_store_compressed=bool
If set, fio will store the log files in a compressed format. They can be
decompressed with fio, using the :option:`--inflate-log` command line
parameter. The files will be stored with a :file:`.fz` suffix.
.. option:: log_unix_epoch=bool
If set, fio will log Unix timestamps to the log files produced by enabling
write_type_log for each log type, instead of the default zero-based
.. option:: block_error_percentiles=bool
If set, record errors in trim block-sized units from writes and trims and
output a histogram of how many trims it took to get to errors, and what kind
of error was encountered.
.. option:: bwavgtime=int
Average the calculated bandwidth over the given time. Value is specified in
milliseconds. If the job also does bandwidth logging through
:option:`write_bw_log`, then the minimum of this option and
:option:`log_avg_msec` will be used. Default: 500ms.
.. option:: iopsavgtime=int
Average the calculated IOPS over the given time. Value is specified in
milliseconds. If the job also does IOPS logging through
:option:`write_iops_log`, then the minimum of this option and
:option:`log_avg_msec` will be used. Default: 500ms.
.. option:: disk_util=bool
Generate disk utilization statistics, if the platform supports it.
Default: true.
.. option:: disable_lat=bool
Disable measurements of total latency numbers. Useful only for cutting back
the number of calls to :manpage:`gettimeofday(2)`, as that does impact
performance at really high IOPS rates. Note that to really get rid of a
large amount of these calls, this option must be used with
:option:`disable_slat` and :option:`disable_bw_measurement` as well.
.. option:: disable_clat=bool
Disable measurements of completion latency numbers. See
.. option:: disable_slat=bool
Disable measurements of submission latency numbers. See
.. option:: disable_bw_measurement=bool, disable_bw=bool
Disable measurements of throughput/bandwidth numbers. See
.. option:: clat_percentiles=bool
Enable the reporting of percentiles of completion latencies.
.. option:: percentile_list=float_list
Overwrite the default list of percentiles for completion latencies and the
block error histogram. Each number is a floating number in the range
(0,100], and the maximum length of the list is 20. Use ``:`` to separate the
numbers, and list the numbers in ascending order. For example,
``--percentile_list=99.5:99.9`` will cause fio to report the values of
completion latency below which 99.5% and 99.9% of the observed latencies
fell, respectively.
Error handling
.. option:: exitall_on_error
When one job finishes in error, terminate the rest. The default is to wait
for each job to finish.
.. option:: continue_on_error=str
Normally fio will exit the job on the first observed failure. If this option
is set, fio will continue the job when there is a 'non-fatal error' (EIO or
EILSEQ) until the runtime is exceeded or the I/O size specified is
completed. If this option is used, there are two more stats that are
appended, the total error count and the first error. The error field given
in the stats is the first error that was hit during the run.
The allowed values are:
Exit on any I/O or verify errors.
Continue on read errors, exit on all others.
Continue on write errors, exit on all others.
Continue on any I/O error, exit on all others.
Continue on verify errors, exit on all others.
Continue on all errors.
Backward-compatible alias for 'none'.
Backward-compatible alias for 'all'.
.. option:: ignore_error=str
Sometimes you want to ignore some errors during test in that case you can
specify error list for each error type.
``ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST`` errors for
given error type is separated with ':'. Error may be symbol ('ENOSPC',
'ENOMEM') or integer. Example::
This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from
.. option:: error_dump=bool
If set dump every error even if it is non fatal, true by default. If
disabled only fatal error will be dumped.
Running predefined workloads
Fio includes predefined profiles that mimic the I/O workloads generated by
other tools.
.. option:: profile=str
The predefined workload to run. Current profiles are:
Threaded I/O bench (tiotest/tiobench) like workload.
Aerospike Certification Tool (ACT) like workload.
To view a profile's additional options use :option:`--cmdhelp` after specifying
the profile. For example::
$ fio --profile=act --cmdhelp
Act profile options
.. option:: device-names=str
Devices to use.
.. option:: load=int
ACT load multiplier. Default: 1.
.. option:: test-duration=time
How long the entire test takes to run. Default: 24h.
.. option:: threads-per-queue=int
Number of read IO threads per device. Default: 8.
.. option:: read-req-num-512-blocks=int
Number of 512B blocks to read at the time. Default: 3.
.. option:: large-block-op-kbytes=int
Size of large block ops in KiB (writes). Default: 131072.
.. option:: prep
Set to run ACT prep phase.
Tiobench profile options
.. option:: size=str
Size in MiB
.. option:: block=int
Block size in bytes. Default: 4096.
.. option:: numruns=int
Number of runs.
.. option:: dir=str
Test directory.
.. option:: threads=int
Number of threads.
Interpreting the output
Fio spits out a lot of output. While running, fio will display the status of the
jobs created. An example of that would be::
Jobs: 1 (f=1): [_(1),M(1)][24.8%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 01m:31s]
The characters inside the square brackets denote the current status of each
thread. The possible values (in typical life cycle order) are:
| Idle | Run | |
| P | | Thread setup, but not started. |
| C | | Thread created. |
| I | | Thread initialized, waiting or generating necessary data. |
| | p | Thread running pre-reading file(s). |
| | R | Running, doing sequential reads. |
| | r | Running, doing random reads. |
| | W | Running, doing sequential writes. |
| | w | Running, doing random writes. |
| | M | Running, doing mixed sequential reads/writes. |
| | m | Running, doing mixed random reads/writes. |
| | F | Running, currently waiting for :manpage:`fsync(2)` |
| | V | Running, doing verification of written data. |
| E | | Thread exited, not reaped by main thread yet. |
| _ | | Thread reaped, or |
| X | | Thread reaped, exited with an error. |
| K | | Thread reaped, exited due to signal. |
Fio will condense the thread string as not to take up more space on the command
line as is needed. For instance, if you have 10 readers and 10 writers running,
the output would look like this::
Jobs: 20 (f=20): [R(10),W(10)][4.0%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 57m:36s]
Fio will still maintain the ordering, though. So the above means that jobs 1..10
are readers, and 11..20 are writers.
The other values are fairly self explanatory -- number of threads currently
running and doing I/O, the number of currently open files (f=), the rate of I/O
since last check (read speed listed first, then write speed and optionally trim
speed), and the estimated completion percentage and time for the current
running group. It's impossible to estimate runtime of the following groups (if
any). Note that the string is displayed in order, so it's possible to tell which
of the jobs are currently doing what. The first character is the first job
defined in the job file, and so forth.
When fio is done (or interrupted by :kbd:`ctrl-c`), it will show the data for
each thread, group of threads, and disks in that order. For each data direction,
the output looks like::
Client1 (g=0): err= 0:
write: io= 32MiB, bw= 666KiB/s, iops=89 , runt= 50320msec
slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
issued r/w: total=0/32768, short=0/0
lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
The client number is printed, along with the group id and error of that
thread. Below is the I/O statistics, here for writes. In the order listed, they
Number of megabytes I/O performed.
Average bandwidth rate.
Average I/Os performed per second.
The runtime of that thread.
Submission latency (avg being the average, stdev being the standard
deviation). This is the time it took to submit the I/O. For sync I/O,
the slat is really the completion latency, since queue/complete is one
operation there. This value can be in milliseconds or microseconds, fio
will choose the most appropriate base and print that. In the example
above, milliseconds is the best scale. Note: in :option:`--minimal` mode
latencies are always expressed in microseconds.
Completion latency. Same names as slat, this denotes the time from
submission to completion of the I/O pieces. For sync I/O, clat will
usually be equal (or very close) to 0, as the time from submit to
complete is basically just CPU time (I/O has already been done, see slat
Bandwidth. Same names as the xlat stats, but also includes an
approximate percentage of total aggregate bandwidth this thread received
in this group. This last value is only really useful if the threads in
this group are on the same disk, since they are then competing for disk
CPU usage. User and system time, along with the number of context
switches this thread went through, usage of system and user time, and
finally the number of major and minor page faults. The CPU utilization
numbers are averages for the jobs in that reporting group, while the
context and fault counters are summed.
**IO depths**
The distribution of I/O depths over the job life time. The numbers are
divided into powers of 2, so for example the 16= entries includes depths
up to that value but higher than the previous entry. In other words, it
covers the range from 16 to 31.
**IO submit**
How many pieces of I/O were submitting in a single submit call. Each
entry denotes that amount and below, until the previous entry -- e.g.,
8=100% mean that we submitted anywhere in between 5-8 I/Os per submit
**IO complete**
Like the above submit number, but for completions instead.
**IO issued**
The number of read/write requests issued, and how many of them were
**IO latencies**
The distribution of I/O completion latencies. This is the time from when
I/O leaves fio and when it gets completed. The numbers follow the same
pattern as the I/O depths, meaning that 2=1.6% means that 1.6% of the
I/O completed within 2 msecs, 20=12.8% means that 12.8% of the I/O took
more than 10 msecs, but less than (or equal to) 20 msecs.
After each client has been listed, the group statistics are printed. They
will look like this::
Run status group 0 (all jobs):
READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
For each data direction, it prints:
Number of megabytes I/O performed.
Aggregate bandwidth of threads in this group.
The minimum average bandwidth a thread saw.
The maximum average bandwidth a thread saw.
The smallest runtime of the threads in that group.
The longest runtime of the threads in that group.
And finally, the disk statistics are printed. They will look like this::
Disk stats (read/write):
sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
Each value is printed for both reads and writes, with reads first. The
numbers denote:
Number of I/Os performed by all groups.
Number of merges I/O the I/O scheduler.
Number of ticks we kept the disk busy.
Total time spent in the disk queue.
The disk utilization. A value of 100% means we kept the disk
busy constantly, 50% would be a disk idling half of the time.
It is also possible to get fio to dump the current output while it is running,
without terminating the job. To do that, send fio the **USR1** signal. You can
also get regularly timed dumps by using the :option:`--status-interval`
parameter, or by creating a file in :file:`/tmp` named
:file:`fio-dump-status`. If fio sees this file, it will unlink it and dump the
current output status.
Terse output
For scripted usage where you typically want to generate tables or graphs of the
results, fio can output the results in a semicolon separated format. The format
is one long line of values, such as::
A description of this job goes here.
The job description (if provided) follows on a second line.
To enable terse output, use the :option:`--minimal` command line option. The
first value is the version of the terse output format. If the output has to be
changed for some reason, this number will be incremented by 1 to signify that
Split up, the format is as follows:
terse version, fio version, jobname, groupid, error
READ status::
Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
Submission latency: min, max, mean, stdev (usec)
Completion latency: min, max, mean, stdev (usec)
Completion latency percentiles: 20 fields (see below)
Total latency: min, max, mean, stdev (usec)
Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev
WRITE status:
Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec)
Submission latency: min, max, mean, stdev (usec)
Completion latency: min, max, mean, stdev(usec)
Completion latency percentiles: 20 fields (see below)
Total latency: min, max, mean, stdev (usec)
Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev
CPU usage::
user, system, context switches, major faults, minor faults
I/O depths::
<=1, 2, 4, 8, 16, 32, >=64
I/O latencies microseconds::
<=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
I/O latencies milliseconds::
<=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
Disk utilization::
Disk name, Read ios, write ios,
Read merges, write merges,
Read ticks, write ticks,
Time spent in queue, disk utilization percentage
Additional Info (dependent on continue_on_error, default off)::
total # errors, first error code
Additional Info (dependent on description being set)::
Text description
Completion latency percentiles can be a grouping of up to 20 sets, so for the
terse output fio writes all of them. Each field will look like this::
which is the Xth percentile, and the `usec` latency associated with it.
For disk utilization, all disks used by fio are shown. So for each disk there
will be a disk utilization section.
Trace file format
There are two trace file format that you can encounter. The older (v1) format is
unsupported since version 1.20-rc3 (March 2008). It will still be described
below in case that you get an old trace and want to understand it.
In any case the trace is a simple text file with a single action per line.
Trace file format v1
Each line represents a single I/O action in the following format::
rw, offset, length
where `rw=0/1` for read/write, and the offset and length entries being in bytes.
This format is not supported in fio versions => 1.20-rc3.
Trace file format v2
The second version of the trace file format was added in fio version 1.17. It
allows to access more then one file per trace and has a bigger set of possible
file actions.
The first line of the trace file has to be::
fio version 2 iolog
Following this can be lines in two different formats, which are described below.
The file management format::
filename action
The filename is given as an absolute path. The action can be one of these:
Add the given filename to the trace.
Open the file with the given filename. The filename has to have
been added with the **add** action before.
Close the file with the given filename. The file has to have been
opened before.
The file I/O action format::
filename action offset length
The `filename` is given as an absolute path, and has to have been added and
opened before it can be used with this format. The `offset` and `length` are
given in bytes. The `action` can be one of these:
Wait for `offset` microseconds. Everything below 100 is discarded.
The time is relative to the previous `wait` statement.
Read `length` bytes beginning from `offset`.
Write `length` bytes beginning from `offset`.
:manpage:`fsync(2)` the file.
:manpage:`fdatasync(2)` the file.
Trim the given file from the given `offset` for `length` bytes.
CPU idleness profiling
In some cases, we want to understand CPU overhead in a test. For example, we
test patches for the specific goodness of whether they reduce CPU usage.
Fio implements a balloon approach to create a thread per CPU that runs at idle
priority, meaning that it only runs when nobody else needs the cpu.
By measuring the amount of work completed by the thread, idleness of each CPU
can be derived accordingly.
An unit work is defined as touching a full page of unsigned characters. Mean and
standard deviation of time to complete an unit work is reported in "unit work"
section. Options can be chosen to report detailed percpu idleness or overall
system idleness by aggregating percpu stats.
Verification and triggers
Fio is usually run in one of two ways, when data verification is done. The first
is a normal write job of some sort with verify enabled. When the write phase has
completed, fio switches to reads and verifies everything it wrote. The second
model is running just the write phase, and then later on running the same job
(but with reads instead of writes) to repeat the same I/O patterns and verify
the contents. Both of these methods depend on the write phase being completed,
as fio otherwise has no idea how much data was written.
With verification triggers, fio supports dumping the current write state to
local files. Then a subsequent read verify workload can load this state and know
exactly where to stop. This is useful for testing cases where power is cut to a
server in a managed fashion, for instance.
A verification trigger consists of two things:
1) Storing the write state of each job.
2) Executing a trigger command.
The write state is relatively small, on the order of hundreds of bytes to single
kilobytes. It contains information on the number of completions done, the last X
completions, etc.
A trigger is invoked either through creation ('touch') of a specified file in
the system, or through a timeout setting. If fio is run with
:option:`--trigger-file` = :file:`/tmp/trigger-file`, then it will continually
check for the existence of :file:`/tmp/trigger-file`. When it sees this file, it
will fire off the trigger (thus saving state, and executing the trigger
For client/server runs, there's both a local and remote trigger. If fio is
running as a server backend, it will send the job states back to the client for
safe storage, then execute the remote trigger, if specified. If a local trigger
is specified, the server will still send back the write state, but the client
will then execute the trigger.
Verification trigger example
Lets say we want to run a powercut test on the remote machine 'server'. Our
write workload is in :file:`write-test.fio`. We want to cut power to 'server' at
some point during the run, and we'll run this test from the safety or our local
machine, 'localbox'. On the server, we'll start the fio backend normally::
server# fio --server
and on the client, we'll fire off the workload::
localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger-remote="bash -c \"echo b > /proc/sysrq-triger\""
We set :file:`/tmp/my-trigger` as the trigger file, and we tell fio to execute::
echo b > /proc/sysrq-trigger
on the server once it has received the trigger and sent us the write state. This
will work, but it's not **really** cutting power to the server, it's merely
abruptly rebooting it. If we have a remote way of cutting power to the server
through IPMI or similar, we could do that through a local trigger command
instead. Lets assume we have a script that does IPMI reboot of a given hostname,
ipmi-reboot. On localbox, we could then have run fio with a local trigger
localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger="ipmi-reboot server"
For this case, fio would wait for the server to send us the write state, then
execute ``ipmi-reboot server`` when that happened.
Loading verify state
To load store write state, read verification job file must contain the
:option:`verify_state_load` option. If that is set, fio will load the previously
stored state. For a local fio run this is done by loading the files directly,
and on a client/server run, the server backend will ask the client to send the
files over and load them from there.
Log File Formats
Fio supports a variety of log file formats, for logging latencies, bandwidth,
and IOPS. The logs share a common format, which looks like this:
*time* (`msec`), *value*, *data direction*, *offset*
Time for the log entry is always in milliseconds. The *value* logged depends
on the type of log, it will be one of the following:
**Latency log**
Value is latency in usecs
**Bandwidth log**
Value is in KiB/sec
**IOPS log**
Value is IOPS
*Data direction* is one of the following:
I/O is a READ
I/O is a WRITE
I/O is a TRIM
The *offset* is the offset, in bytes, from the start of the file, for that
particular I/O. The logging of the offset can be toggled with
If windowed logging is enabled through :option:`log_avg_msec` then fio doesn't
log individual I/Os. Instead of logs the average values over the specified period
of time. Since 'data direction' and 'offset' are per-I/O values, they aren't
applicable if windowed logging is enabled. If windowed logging is enabled and
:option:`log_max_value` is set, then fio logs maximum values in that window
instead of averages.
Normally fio is invoked as a stand-alone application on the machine where the
I/O workload should be generated. However, the frontend and backend of fio can
be run separately. Ie the fio server can generate an I/O workload on the "Device
Under Test" while being controlled from another machine.
Start the server on the machine which has access to the storage DUT::
fio --server=args
where args defines what fio listens to. The arguments are of the form
``type,hostname`` or ``IP,port``. *type* is either ``ip`` (or ip4) for TCP/IP
v4, ``ip6`` for TCP/IP v6, or ``sock`` for a local unix domain socket.
*hostname* is either a hostname or IP address, and *port* is the port to listen
to (only valid for TCP/IP, not a local socket). Some examples:
1) ``fio --server``
Start a fio server, listening on all interfaces on the default port (8765).
2) ``fio --server=ip:hostname,4444``
Start a fio server, listening on IP belonging to hostname and on port 4444.
3) ``fio --server=ip6:::1,4444``
Start a fio server, listening on IPv6 localhost ::1 and on port 4444.
4) ``fio --server=,4444``
Start a fio server, listening on all interfaces on port 4444.
5) ``fio --server=``
Start a fio server, listening on IP on the default port.
6) ``fio --server=sock:/tmp/fio.sock``
Start a fio server, listening on the local socket /tmp/fio.sock.
Once a server is running, a "client" can connect to the fio server with::
fio <local-args> --client=<server> <remote-args> <job file(s)>
where `local-args` are arguments for the client where it is running, `server`
is the connect string, and `remote-args` and `job file(s)` are sent to the
server. The `server` string follows the same format as it does on the server
side, to allow IP/hostname/socket and port strings.
Fio can connect to multiple servers this way::
fio --client=<server1> <job file(s)> --client=<server2> <job file(s)>
If the job file is located on the fio server, then you can tell the server to
load a local file as well. This is done by using :option:`--remote-config` ::
fio --client=server --remote-config /path/to/file.fio
Then fio will open this local (to the server) job file instead of being passed
one from the client.
If you have many servers (example: 100 VMs/containers), you can input a pathname
of a file containing host IPs/names as the parameter value for the
:option:`--client` option. For example, here is an example :file:`host.list`
file containing 2 hostnames::
The fio command would then be::
fio --client=host.list <job file(s)>
In this mode, you cannot input server-specific parameters or job files -- all
servers receive the same job file.
In order to let ``fio --client`` runs use a shared filesystem from multiple
hosts, ``fio --client`` now prepends the IP address of the server to the
filename. For example, if fio is using directory :file:`/mnt/nfs/fio` and is
writing filename :file:`fileio.tmp`, with a :option:`--client` `hostfile`
containing two hostnames ``h1`` and ``h2`` with IP addresses and, then fio will create two files::