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.
a string. The following types are used:
str String. This is a sequence of alpha characters.
-int Integer. A whole number value, may be negative.
+int Integer. A whole number value, can be negative.
siint SI integer. A whole number value, which may contain a postfix
describing the base of the number. Accepted postfixes are k/m/g,
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. '-' is a reserved
+ name, meaning stdin or stdout. Which of the two depends
+ on the read/write direction set.
+
+opendir=str Tell fio to recursively add any file it can find in this
+ directory and down the file system tree.
+
+readwrite=str
rw=str Type of io pattern. Accepted values are:
read Sequential reads
For the mixed io types, the default is to split them 50/50.
For certain types of io the result may still be skewed a bit,
- since the speed may be different.
+ since the speed may be different. It is possible to specify
+ a number of IO's to do before getting a new offset - this
+ is only useful for random IO, where fio would normally
+ generate a new random offset for every IO. If you append
+ eg 8 to randread, you would get a new random offset for
+ every 8 IO's. The result would be a seek for only every 8
+ IO's, instead of for every IO. Use rw=randread:8 to specify
+ that.
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
- file already exists, the file size will be adjusted to this
- size if larger than the current file size. If this parameter
- is not given and the file exists, the file size will be used.
-
+fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
+ on what IO patterns it is likely to issue. Sometimes you
+ want to test specific IO patterns without telling the
+ kernel about it, in which case you can disable this option.
+ If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
+ IO and POSIX_FADV_RANDOM for random IO.
+
+size=siint The total size of file io for this job. Fio will run until
+ this many bytes has been transferred, unless runtime is
+ limited by other options (such as 'runtime', for instance).
+ Unless specific nr_files and filesize options are given,
+ fio will divide this size between the available files
+ specified by the job.
+
+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.
+
+blocksize=siint
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
can do so by passing an empty read size - bs=,8k will set
8k for writes and leave the read default value.
+blocksize_range=irange
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
writes, however a second range can be given after a comma.
See bs=.
+blocksize_unaligned
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
direct IO, as that normally requires sector alignment.
+zero_buffers If this option is given, fio will init the IO buffers to
+ all zeroes. The default is to fill them with random data.
+
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
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.
+
+ guasi The GUASI IO engine is the Generic Userspace
+ Asyncronous Syscall Interface approach
+ to async IO. See
+
+ http://www.xmailserver.org/guasi-lib.html
+
+ for more info on GUASI.
+
+ 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.
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.
new random offset without looking at past io history. This
means that some blocks may not be read or written, and that
some blocks may be read/written more than once. This option
- is mutually exclusive with verify= for that reason.
+ is mutually exclusive with verify= for that reason, since
+ fio doesn't track potential block rewrites which may alter
+ the calculated checksum for that block.
nice=int Run the job with the given nice value. See man nice(2).
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. See thinktime_blocks.
+ 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
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.
cpumask=int Set the CPU affinity of this job. The parameter given is a
bitmask of allowed CPU's the job may run on. See man
- sched_setaffinity(2).
+ sched_setaffinity(2). This may not work on all supported
+ operating systems or kernel versions.
startdelay=int Start this job the specified number of seconds after fio
has started. Only useful if the job file contains several
a specified job will run, so this parameter is handy to
cap the total runtime to a given time.
+time_based If set, fio will run for the duration of the runtime
+ specified even if the file(s) are completey read or
+ written. It will simply loop over the same workload
+ as many times as the runtime allows.
+
invalidate=bool Invalidate the buffer/page cache parts for this file prior
to starting io. Defaults to true.
sync=bool Use sync io for buffered writes. For the majority of the
io engines, this means using O_SYNC.
+iomem=str
mem=str Fio can use various types of memory as the io unit buffer.
The allowed values are:
create_fsync=bool fsync the data file after creation. This is the
default.
-unlink=bool 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
crc32 Use a crc32 sum of the data area and store
it in the header of each block.
+ null Only pretend to verify. Useful for testing
+ internals with 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.
+verifysort=bool If set, 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 IO where the red-black tree sorting CPU time becomes
+ significant.
+
stonewall Wait for preceeding jobs in the job file to exit, before
starting this one. Can be used to insert serialization
- points in the job file.
+ points in the job file. A stone wall also implies starting
+ a new reporting group.
+
+new_group Start a new reporting group. If this option isn't given,
+ jobs in a file will be part of the same reporting group
+ unless seperated by a stone wall (or if it's a group
+ by itself, with the numjobs option).
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
read_iolog=str Open an iolog with the specified file name and replay the
io patterns it contains. This can be used to store a
- workload and replay it sometime later.
+ 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 blktrace. See blktrace
+ for how to capture such logging data. For blktrace replay,
+ the file needs to be turned into a blkparse binary data
+ file first (blktrace <device> -d file_for_fio.bin).
write_bw_log If given, write a bandwidth log of the jobs in this job
file. Can be used to store data of the bandwidth of the
cpuchunks=int If the job is a CPU cycle eater, split the load into
cycles of the given time. In milliseconds.
+disk_util=bool Generate disk utilization statistics, if the platform
+ supports it. Defaults to on.
+
6.0 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:
-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:
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%
+ 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 io statistics, here for writes. In the order listed,
io= Number of megabytes io performed
bw= Average bandwidth rate
runt= The runtime of that thread
- slat= Submission latency (avg being the average, dev being the
+ slat= Submission latency (avg being the average, stdev being the
standard deviation). This is the time it took to submit
the io. For sync io, the slat is really the completion
latency, since queue/complete is one operation there.
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 issued= The number of read/write requests issued, and how many
+ of them were short.
+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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