IO engine How do we issue io? We could be memory mapping the
file, we could be using regular read/write, we
- could be using splice, async io, or even
+ could be using splice, async io, syslet, or even
SG (SCSI generic sg).
IO depth If the io engine is async, how large a queuing
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. If the first character in a line is a ';', the
-entire line is discarded as a comment.
+section residing above it. If the first character in a line is a ';' or a
+'#', the entire line is discarded as a comment.
So lets look at a really simple job file that define to threads, each
randomly reading from a 128MiB file.
meaning kilo, mega, and giga. So if you want to specify 4096,
you could either write out '4096' or just give 4k. The postfixes
signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
+ If the option accepts an upper and lower range, use a colon ':'
+ or minus '-' to seperate such values. See irange.
bool Boolean. Usually parsed as an integer, however only defined for
true and false (1 and 0).
irange Integer range with postfix. Allows value range to be given, such
- as 1024-4096. Also see siint.
+ as 1024-4096. A colon may also be used as the seperator, eg
+ 1k:4k. If the option allows two sets of ranges, they can be
+ specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
+ siint.
With the above in mind, here follows the complete list of fio job
parameters.
special purpose of also signaling the start of a new
job.
+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.
+
directory=str Prefix filenames with this directory. Used to places files
in a different location than "./".
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, specify
- a filename for each of them to override the default.
+ a filename for each of them to override the default. If
+ the ioengine used is 'net', the filename is the host and
+ port to connect to in the format of =host/port. If the
+ ioengine is file based, you can specify a number of files
+ by seperating the names with a ':' colon. So if you wanted
+ a job to open /dev/sda and /dev/sdb as the two working files,
+ you would use filename=/dev/sda:/dev/sdb
+
+opendir=str Tell fio to recursively add any file it can find in this
+ directory and down the file system tree.
rw=str Type of io pattern. Accepted values are:
For certain types of io the result may still be skewed a bit,
since the speed may be different.
+randrepeat=bool For random IO workloads, seed the generator in a predictable
+ way so that results are repeatable across repetitions.
+
size=siint The total size of file io for this job. This may describe
the size of the single file the job uses, or it may be
divided between the number of files in the job. If the
size if larger than the current file size. If this parameter
is not given and the file exists, the file size will be used.
-bs=siint The block size used for the io units. Defaults to 4k.
-
-read_bs=siint
-write_bs=siint If the workload is a mixed read-write workload, you can use
- these options to set separate block sizes.
+filesize=siint 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 'size' in total (if that is given). If not
+ given, each created file is the same size.
+
+bs=siint The block size used for the io units. Defaults to 4k. Values
+ can be given for both read and writes. If a single siint is
+ given, it will apply to both. If a second siint is specified
+ after a comma, it will apply to writes only. In other words,
+ the format is either bs=read_and_write or bs=read,write.
+ bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
+ for writes. If you only wish to set the write size, you
+ can do so by passing an empty read size - bs=,8k will set
+ 8k for writes and leave the read default value.
bsrange=irange Instead of giving a single block size, specify a range
and fio will mix the issued io block sizes. The issued
io unit will always be a multiple of the minimum value
- given (also see bs_unaligned).
-
-read_bsrange=irange
-write_bsrange=irange
- If the workload is a mixed read-write workload, you can use
- one of these options to set separate block size ranges for
- reads and writes.
+ given (also see bs_unaligned). Applies to both reads and
+ writes, however a second range can be given after a comma.
+ See bs=.
bs_unaligned If this option is given, any byte size value within bsrange
may be used as a block range. This typically wont work with
nrfiles=int Number of files to use for this job. Defaults to 1.
+openfiles=int Number of files to keep open at the same time. Defaults to
+ the same as nrfiles, can be set smaller to limit the number
+ simultaneous opens.
+
+file_service_type=str Defines how fio decides which file from a job to
+ service next. The following types are defined:
+
+ random Just choose a file at random.
+
+ roundrobin Round robin over open files. This
+ is the default.
+
+ The string can have a number appended, indicating how
+ often to switch to a new file. So if option random:4 is
+ given, fio will switch to a new random file after 4 ios
+ have been issued.
+
ioengine=str Defines how the job issues io to the file. The following
types are defined:
vmsplice(2) to transfer data from user
space to the kernel.
+ syslet-rw Use the syslet system calls to make
+ regular read/write async.
+
sg SCSI generic sg v3 io. May either be
synchronous using the SG_IO ioctl, or if
the target is an sg character device
we use read(2) and write(2) for asynchronous
io.
+ null Doesn't transfer any data, just pretends
+ to. This is mainly used to exercise fio
+ itself and for debugging/testing purposes.
+
+ net Transfer over the network to given host:port.
+ 'filename' must be set appropriately to
+ filename=host/port regardless of send
+ or receive, if the latter only the port
+ argument is used.
+
+ cpu Doesn't transfer any data, but burns CPU
+ cycles according to the cpuload= and
+ cpucycle= options. Setting cpuload=85
+ will cause that job to do nothing but burn
+ 85% of the CPU.
+
+ external Prefix to specify loading an external
+ IO engine object file. Append the engine
+ filename, eg ioengine=external:/tmp/foo.o
+ to load ioengine foo.o in /tmp.
+
iodepth=int This defines how many io units to keep in flight against
the file. The default is 1 for each file defined in this
job, can be overridden with a larger value for higher
concurrency.
+iodepth_batch=int This defines how many pieces of IO to submit at once.
+ It defaults to the same as iodepth, but can be set lower
+ if one so desires.
+
+iodepth_low=int The low water mark indicating when to start filling
+ the queue again. Defaults to the same as iodepth, meaning
+ that fio will attempt to keep the queue full at all times.
+ If iodepth is set to eg 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.
+
direct=bool If value is true, use non-buffered io. This is usually
- O_DIRECT. Defaults to true.
+ O_DIRECT.
+
+buffered=bool If value is true, use buffered io. This is the opposite
+ of the 'direct' option. Defaults to true.
offset=siint Start io at the given offset in the file. The data before
the given offset will not be touched. This effectively
end_fsync=bool If true, fsync file contents when the job exits.
+fsync_on_close=bool If true, fio will fsync() 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.
+
rwmixcycle=int Value in milliseconds describing how often to switch between
reads and writes for a mixed workload. The default is
500 msecs.
thinktime=int Stall the job x microseconds after an io has completed before
issuing the next. May be used to simulate processing being
- done by an application.
+ done by an application. See thinktime_blocks and
+ thinktime_spin.
+
+thinktime_spin=int
+ Only valid if 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
+ thinktime.
+
+thinktime_blocks
+ Only valid if 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.
rate=int Cap the bandwidth used by this job to this number of KiB/sec.
ratemin=int Tell fio to do whatever it can to maintain at least this
- bandwidth.
+ bandwidth. Failing to meet this requirement, will cause
+ the job to exit.
+
+rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
+ as 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.
+
+rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
+ the job to exit.
ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
of milliseconds.
jobs, and you want to delay starting some jobs to a certain
time.
-timeout=int Tell fio to terminate processing after the specified number
+runtime=int Tell fio to terminate processing after the specified number
of seconds. 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.
shm Use shared memory as the buffers. Allocated
through shmget(2).
- mmap Use anonymous memory maps as the buffers.
- Allocated through mmap(2).
+ shmhuge Same as shm, but use huge pages as backing.
+
+ mmap 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.
+
+ mmaphuge Use a memory mapped huge file as the buffer
+ backing. Append filename after mmaphuge, ala
+ mem=mmaphuge:/hugetlbfs/file
The area allocated is a function of the maximum allowed
- bs size for the job, multiplied by the io depth given.
+ bs size for the job, multiplied by the io 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 /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 io depth of all jobs (normally one unless
+ 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 /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 hugepage-size.
+
+ mmaphuge also needs to have hugetlbfs mounted and the file
+ location should point there. So if it's mounted in /huge,
+ you would use mem=mmaphuge:/huge/somefile.
+
+hugepage-size=siint
+ Defines the size of a huge page. Must at least be equal
+ to the system setting, see /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.
exitall When one job finishes, terminate the rest. The default is
to wait for each job to finish, sometimes that is not the
create_fsync=bool fsync the data file after creation. This is the
default.
-unlink Unlink the job files when done. fio defaults to doing this,
- if it created the file itself.
+unlink=bool Unlink the job files when done. Not the default, as repeated
+ runs of that job would then waste time recreating the fileset
+ again and again.
loops=int Run the specified number of iterations of this job. Used
to repeat the same workload a given number of times. Defaults
numjobs=int Create the specified number of clones of this job. May be
used to setup a larger number of threads/processes doing
- the same thing.
+ the same thing. We regard that grouping of jobs as a
+ specific group.
+
+group_reporting If 'numjobs' is set, it may be interesting to display
+ statistics for the group as a whole instead of for each
+ individual job. This is especially true of 'numjobs' is
+ large, looking at individual thread/process output quickly
+ becomes unwieldy. If 'group_reporting' is specified, fio
+ will show the final report per-group instead of per-job.
thread fio defaults to forking jobs, however if this option is
given, fio will use pthread_create(3) to create threads
fio spits out a lot of output. While running, fio will display the
status of the jobs created. An example of that would be:
-Threads running: 1: [_r] [24.79% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
+Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
The characters inside the square brackets denote the current status of
each thread. The possible values (in typical life cycle order) are:
Client1 (g=0): err= 0:
write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
- slat (msec): min= 0, max= 136, avg= 0.03, dev= 1.92
- clat (msec): min= 0, max= 631, avg=48.50, dev=86.82
- bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, dev=681.68
+ 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
+ IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=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 io statistics, here for writes. In the order listed,
same disk, since they are then competing for disk access.
cpu= CPU usage. User and system time, along with the number
of context switches this thread went through.
+IO depths= The distribution of io 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 latencies= The distribution of IO completion latencies. This is the
+ time from when IO leaves fio and when it gets completed.
+ The numbers follow the same pattern as the IO depths,
+ meaning that 2=1.6% means that 1.6% of the IO completed
+ within 2 msecs, 20=12.8% means that 12.8% of the IO
+ 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:
----------------
For scripted usage where you typically want to generate tables or graphs
-of the results, fio can output the results in a comma separated format.
+of the results, fio can output the results in a semicolon separated format.
The format is one long line of values, such as:
-client1,0,0,936,331,2894,0,0,0.000000,0.000000,1,170,22.115385,34.290410,16,714,84.252874%,366.500000,566.417819,3496,1237,2894,0,0,0.000000,0.000000,0,246,6.671625,21.436952,0,2534,55.465300%,1406.600000,2008.044216,0.000000%,0.431928%,1109
+client1;0;0;1906777;1090804;1790;0;0;0.000000;0.000000;0;0;0.000000;0.000000;929380;1152890;25.510151%;1078276.333333;128948.113404;0;0;0;0;0;0.000000;0.000000;0;0;0.000000;0.000000;0;0;0.000000%;0.000000;0.000000;100.000000%;0.000000%;324;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%;0.0%;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%
+;0.0%;0.0%;0.0%;0.0%;0.0%
Split up, the format is as follows:
Completion latency: min, max, mean, deviation
Bw: min, max, aggregate percentage of total, mean, deviation
CPU usage: user, system, context switches
+ IO depths: <=1, 2, 4, 8, 16, 32, >=64
+ IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000
+ Text description
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