8 5. Detailed list of parameters
13 1.0 Overview and history
14 ------------------------
15 fio was originally written to save me the hassle of writing special test
16 case programs when I wanted to test a specific workload, either for
17 performance reasons or to find/reproduce a bug. The process of writing
18 such a test app can be tiresome, especially if you have to do it often.
19 Hence I needed a tool that would be able to simulate a given io workload
20 without resorting to writing a tailored test case again and again.
22 A test work load is difficult to define, though. There can be any number
23 of processes or threads involved, and they can each be using their own
24 way of generating io. You could have someone dirtying large amounts of
25 memory in an memory mapped file, or maybe several threads issuing
26 reads using asynchronous io. fio needed to be flexible enough to
27 simulate both of these cases, and many more.
31 The first step in getting fio to simulate a desired io workload, is
32 writing a job file describing that specific setup. A job file may contain
33 any number of threads and/or files - the typical contents of the job file
34 is a global section defining shared parameters, and one or more job
35 sections describing the jobs involved. When run, fio parses this file
36 and sets everything up as described. If we break down a job from top to
37 bottom, it contains the following basic parameters:
39 IO type Defines the io pattern issued to the file(s).
40 We may only be reading sequentially from this
41 file(s), or we may be writing randomly. Or even
42 mixing reads and writes, sequentially or randomly.
44 Block size In how large chunks are we issuing io? This may be
45 a single value, or it may describe a range of
48 IO size How much data are we going to be reading/writing.
50 IO engine How do we issue io? We could be memory mapping the
51 file, we could be using regular read/write, we
52 could be using splice, async io, syslet, or even
55 IO depth If the io engine is async, how large a queuing
56 depth do we want to maintain?
58 IO type Should we be doing buffered io, or direct/raw io?
60 Num files How many files are we spreading the workload over.
62 Num threads How many threads or processes should we spread
65 The above are the basic parameters defined for a workload, in addition
66 there's a multitude of parameters that modify other aspects of how this
72 See the README file for command line parameters, there are only a few
75 Running fio is normally the easiest part - you just give it the job file
76 (or job files) as parameters:
80 and it will start doing what the job_file tells it to do. You can give
81 more than one job file on the command line, fio will serialize the running
82 of those files. Internally that is the same as using the 'stonewall'
83 parameter described the the parameter section.
85 If the job file contains only one job, you may as well just give the
86 parameters on the command line. The command line parameters are identical
87 to the job parameters, with a few extra that control global parameters
88 (see README). For example, for the job file parameter iodepth=2, the
89 mirror command line option would be --iodepth 2 or --iodepth=2. You can
90 also use the command line for giving more than one job entry. For each
91 --name option that fio sees, it will start a new job with that name.
92 Command line entries following a --name entry will apply to that job,
93 until there are no more entries or a new --name entry is seen. This is
94 similar to the job file options, where each option applies to the current
95 job until a new [] job entry is seen.
97 fio does not need to run as root, except if the files or devices specified
98 in the job section requires that. Some other options may also be restricted,
99 such as memory locking, io scheduler switching, and decreasing the nice value.
104 As previously described, fio accepts one or more job files describing
105 what it is supposed to do. The job file format is the classic ini file,
106 where the names enclosed in [] brackets define the job name. You are free
107 to use any ascii name you want, except 'global' which has special meaning.
108 A global section sets defaults for the jobs described in that file. A job
109 may override a global section parameter, and a job file may even have
110 several global sections if so desired. A job is only affected by a global
111 section residing above it. If the first character in a line is a ';' or a
112 '#', the entire line is discarded as a comment.
114 So lets look at a really simple job file that define to threads, each
115 randomly reading from a 128MiB file.
117 ; -- start job file --
128 As you can see, the job file sections themselves are empty as all the
129 described parameters are shared. As no filename= option is given, fio
130 makes up a filename for each of the jobs as it sees fit. On the command
131 line, this job would look as follows:
133 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
136 Lets look at an example that have a number of processes writing randomly
139 ; -- start job file --
151 Here we have no global section, as we only have one job defined anyway.
152 We want to use async io here, with a depth of 4 for each file. We also
153 increased the buffer size used to 32KiB and define numjobs to 4 to
154 fork 4 identical jobs. The result is 4 processes each randomly writing
155 to their own 64MiB file. Instead of using the above job file, you could
156 have given the parameters on the command line. For this case, you would
159 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
161 fio ships with a few example job files, you can also look there for
165 5.0 Detailed list of parameters
166 -------------------------------
168 This section describes in details each parameter associated with a job.
169 Some parameters take an option of a given type, such as an integer or
170 a string. The following types are used:
172 str String. This is a sequence of alpha characters.
173 int Integer. A whole number value, may be negative.
174 siint SI integer. A whole number value, which may contain a postfix
175 describing the base of the number. Accepted postfixes are k/m/g,
176 meaning kilo, mega, and giga. So if you want to specify 4096,
177 you could either write out '4096' or just give 4k. The postfixes
178 signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
179 bool Boolean. Usually parsed as an integer, however only defined for
180 true and false (1 and 0).
181 irange Integer range with postfix. Allows value range to be given, such
182 as 1024-4096. A colon may also be used as the seperator, eg
183 1k:4k. If the option allows two sets of ranges, they can be
184 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
187 With the above in mind, here follows the complete list of fio job
190 name=str ASCII name of the job. This may be used to override the
191 name printed by fio for this job. Otherwise the job
192 name is used. On the command line this parameter has the
193 special purpose of also signaling the start of a new
196 description=str Text description of the job. Doesn't do anything except
197 dump this text description when this job is run. It's
200 directory=str Prefix filenames with this directory. Used to places files
201 in a different location than "./".
203 filename=str Fio normally makes up a filename based on the job name,
204 thread number, and file number. If you want to share
205 files between threads in a job or several jobs, specify
206 a filename for each of them to override the default. If
207 the ioengine used is 'net', the filename is the host and
208 port to connect to in the format of =host/port. If the
209 ioengine is file based, you can specify a number of files
210 by seperating the names with a ':' colon. So if you wanted
211 a job to open /dev/sda and /dev/sdb as the two working files,
212 you would use filename=/dev/sda:/dev/sdb
214 rw=str Type of io pattern. Accepted values are:
216 read Sequential reads
217 write Sequential writes
218 randwrite Random writes
219 randread Random reads
220 rw Sequential mixed reads and writes
221 randrw Random mixed reads and writes
223 For the mixed io types, the default is to split them 50/50.
224 For certain types of io the result may still be skewed a bit,
225 since the speed may be different.
227 randrepeat=bool For random IO workloads, seed the generator in a predictable
228 way so that results are repeatable across repetitions.
230 size=siint The total size of file io for this job. This may describe
231 the size of the single file the job uses, or it may be
232 divided between the number of files in the job. If the
233 file already exists, the file size will be adjusted to this
234 size if larger than the current file size. If this parameter
235 is not given and the file exists, the file size will be used.
237 bs=siint The block size used for the io units. Defaults to 4k. Values
238 can be given for both read and writes. If a single siint is
239 given, it will apply to both. If a second siint is specified
240 after a comma, it will apply to writes only. In other words,
241 the format is either bs=read_and_write or bs=read,write.
242 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
243 for writes. If you only wish to set the write size, you
244 can do so by passing an empty read size - bs=,8k will set
245 8k for writes and leave the read default value.
247 bsrange=irange Instead of giving a single block size, specify a range
248 and fio will mix the issued io block sizes. The issued
249 io unit will always be a multiple of the minimum value
250 given (also see bs_unaligned). Applies to both reads and
251 writes, however a second range can be given after a comma.
254 bs_unaligned If this option is given, any byte size value within bsrange
255 may be used as a block range. This typically wont work with
256 direct IO, as that normally requires sector alignment.
258 nrfiles=int Number of files to use for this job. Defaults to 1.
260 openfiles=int Number of files to keep open at the same time. Defaults to
261 the same as nrfiles, can be set smaller to limit the number
264 file_service_type=str Defines how fio decides which file from a job to
265 service next. The following types are defined:
267 random Just choose a file at random.
269 roundrobin Round robin over open files. This
272 The string can have a number appended, indicating how
273 often to switch to a new file. So if option random:4 is
274 given, fio will switch to a new random file after 4 ios
277 ioengine=str Defines how the job issues io to the file. The following
280 sync Basic read(2) or write(2) io. lseek(2) is
281 used to position the io location.
283 libaio Linux native asynchronous io.
285 posixaio glibc posix asynchronous io.
287 mmap File is memory mapped and data copied
288 to/from using memcpy(3).
290 splice splice(2) is used to transfer the data and
291 vmsplice(2) to transfer data from user
294 syslet-rw Use the syslet system calls to make
295 regular read/write async.
297 sg SCSI generic sg v3 io. May either be
298 synchronous using the SG_IO ioctl, or if
299 the target is an sg character device
300 we use read(2) and write(2) for asynchronous
303 null Doesn't transfer any data, just pretends
304 to. This is mainly used to exercise fio
305 itself and for debugging/testing purposes.
307 net Transfer over the network to given host:port.
308 'filename' must be set appropriately to
309 filename=host/port regardless of send
310 or receive, if the latter only the port
313 cpu Doesn't transfer any data, but burns CPU
314 cycles according to the cpuload= and
315 cpucycle= options. Setting cpuload=85
316 will cause that job to do nothing but burn
319 external Prefix to specify loading an external
320 IO engine object file. Append the engine
321 filename, eg ioengine=external:/tmp/foo.o
322 to load ioengine foo.o in /tmp.
324 iodepth=int This defines how many io units to keep in flight against
325 the file. The default is 1 for each file defined in this
326 job, can be overridden with a larger value for higher
329 iodepth_batch=int This defines how many pieces of IO to submit at once.
330 It defaults to the same as iodepth, but can be set lower
333 iodepth_low=int The low water mark indicating when to start filling
334 the queue again. Defaults to the same as iodepth, meaning
335 that fio will attempt to keep the queue full at all times.
336 If iodepth is set to eg 16 and iodepth_low is set to 4, then
337 after fio has filled the queue of 16 requests, it will let
338 the depth drain down to 4 before starting to fill it again.
340 direct=bool If value is true, use non-buffered io. This is usually
343 buffered=bool If value is true, use buffered io. This is the opposite
344 of the 'direct' option. Defaults to true.
346 offset=siint Start io at the given offset in the file. The data before
347 the given offset will not be touched. This effectively
348 caps the file size at real_size - offset.
350 fsync=int If writing to a file, issue a sync of the dirty data
351 for every number of blocks given. For example, if you give
352 32 as a parameter, fio will sync the file for every 32
353 writes issued. If fio is using non-buffered io, we may
354 not sync the file. The exception is the sg io engine, which
355 synchronizes the disk cache anyway.
357 overwrite=bool If writing to a file, setup the file first and do overwrites.
359 end_fsync=bool If true, fsync file contents when the job exits.
361 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
362 This differs from end_fsync in that it will happen on every
363 file close, not just at the end of the job.
365 rwmixcycle=int Value in milliseconds describing how often to switch between
366 reads and writes for a mixed workload. The default is
369 rwmixread=int How large a percentage of the mix should be reads.
371 rwmixwrite=int How large a percentage of the mix should be writes. If both
372 rwmixread and rwmixwrite is given and the values do not add
373 up to 100%, the latter of the two will be used to override
376 norandommap Normally fio will cover every block of the file when doing
377 random IO. If this option is given, fio will just get a
378 new random offset without looking at past io history. This
379 means that some blocks may not be read or written, and that
380 some blocks may be read/written more than once. This option
381 is mutually exclusive with verify= for that reason.
383 nice=int Run the job with the given nice value. See man nice(2).
385 prio=int Set the io priority value of this job. Linux limits us to
386 a positive value between 0 and 7, with 0 being the highest.
389 prioclass=int Set the io priority class. See man ionice(1).
391 thinktime=int Stall the job x microseconds after an io has completed before
392 issuing the next. May be used to simulate processing being
393 done by an application. See thinktime_blocks and
397 Only valid if thinktime is set - pretend to spend CPU time
398 doing something with the data received, before falling back
399 to sleeping for the rest of the period specified by
403 Only valid if thinktime is set - control how many blocks
404 to issue, before waiting 'thinktime' usecs. If not set,
405 defaults to 1 which will make fio wait 'thinktime' usecs
408 rate=int Cap the bandwidth used by this job to this number of KiB/sec.
410 ratemin=int Tell fio to do whatever it can to maintain at least this
413 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
416 cpumask=int Set the CPU affinity of this job. The parameter given is a
417 bitmask of allowed CPU's the job may run on. See man
418 sched_setaffinity(2).
420 startdelay=int Start this job the specified number of seconds after fio
421 has started. Only useful if the job file contains several
422 jobs, and you want to delay starting some jobs to a certain
425 runtime=int Tell fio to terminate processing after the specified number
426 of seconds. It can be quite hard to determine for how long
427 a specified job will run, so this parameter is handy to
428 cap the total runtime to a given time.
430 invalidate=bool Invalidate the buffer/page cache parts for this file prior
431 to starting io. Defaults to true.
433 sync=bool Use sync io for buffered writes. For the majority of the
434 io engines, this means using O_SYNC.
436 mem=str Fio can use various types of memory as the io unit buffer.
437 The allowed values are:
439 malloc Use memory from malloc(3) as the buffers.
441 shm Use shared memory as the buffers. Allocated
444 shmhuge Same as shm, but use huge pages as backing.
446 mmap Use mmap to allocate buffers. May either be
447 anonymous memory, or can be file backed if
448 a filename is given after the option. The
449 format is mem=mmap:/path/to/file.
451 mmaphuge Use a memory mapped huge file as the buffer
452 backing. Append filename after mmaphuge, ala
453 mem=mmaphuge:/hugetlbfs/file
455 The area allocated is a function of the maximum allowed
456 bs size for the job, multiplied by the io depth given. Note
457 that for shmhuge and mmaphuge to work, the system must have
458 free huge pages allocated. This can normally be checked
459 and set by reading/writing /proc/sys/vm/nr_hugepages on a
460 Linux system. Fio assumes a huge page is 4MiB in size. So
461 to calculate the number of huge pages you need for a given
462 job file, add up the io depth of all jobs (normally one unless
463 iodepth= is used) and multiply by the maximum bs set. Then
464 divide that number by the huge page size. You can see the
465 size of the huge pages in /proc/meminfo. If no huge pages
466 are allocated by having a non-zero number in nr_hugepages,
467 using mmaphuge or shmhuge will fail. Also see hugepage-size.
469 mmaphuge also needs to have hugetlbfs mounted and the file
470 location should point there. So if it's mounted in /huge,
471 you would use mem=mmaphuge:/huge/somefile.
474 Defines the size of a huge page. Must at least be equal
475 to the system setting, see /proc/meminfo. Defaults to 4MiB.
476 Should probably always be a multiple of megabytes, so using
477 hugepage-size=Xm is the preferred way to set this to avoid
478 setting a non-pow-2 bad value.
480 exitall When one job finishes, terminate the rest. The default is
481 to wait for each job to finish, sometimes that is not the
484 bwavgtime=int Average the calculated bandwidth over the given time. Value
485 is specified in milliseconds.
487 create_serialize=bool If true, serialize the file creating for the jobs.
488 This may be handy to avoid interleaving of data
489 files, which may greatly depend on the filesystem
490 used and even the number of processors in the system.
492 create_fsync=bool fsync the data file after creation. This is the
495 unlink=bool Unlink the job files when done. Not the default, as repeated
496 runs of that job would then waste time recreating the fileset
499 loops=int Run the specified number of iterations of this job. Used
500 to repeat the same workload a given number of times. Defaults
503 verify=str If writing to a file, fio can verify the file contents
504 after each iteration of the job. The allowed values are:
506 md5 Use an md5 sum of the data area and store
507 it in the header of each block.
509 crc32 Use a crc32 sum of the data area and store
510 it in the header of each block.
512 This option can be used for repeated burn-in tests of a
513 system to make sure that the written data is also
516 stonewall Wait for preceeding jobs in the job file to exit, before
517 starting this one. Can be used to insert serialization
518 points in the job file.
520 numjobs=int Create the specified number of clones of this job. May be
521 used to setup a larger number of threads/processes doing
522 the same thing. We regard that grouping of jobs as a
525 group_reporting If 'numjobs' is set, it may be interesting to display
526 statistics for the group as a whole instead of for each
527 individual job. This is especially true of 'numjobs' is
528 large, looking at individual thread/process output quickly
529 becomes unwieldy. If 'group_reporting' is specified, fio
530 will show the final report per-group instead of per-job.
532 thread fio defaults to forking jobs, however if this option is
533 given, fio will use pthread_create(3) to create threads
536 zonesize=siint Divide a file into zones of the specified size. See zoneskip.
538 zoneskip=siint Skip the specified number of bytes when zonesize data has
539 been read. The two zone options can be used to only do
540 io on zones of a file.
542 write_iolog=str Write the issued io patterns to the specified file. See
545 read_iolog=str Open an iolog with the specified file name and replay the
546 io patterns it contains. This can be used to store a
547 workload and replay it sometime later.
549 write_bw_log If given, write a bandwidth log of the jobs in this job
550 file. Can be used to store data of the bandwidth of the
551 jobs in their lifetime. The included fio_generate_plots
552 script uses gnuplot to turn these text files into nice
555 write_lat_log Same as write_bw_log, except that this option stores io
556 completion latencies instead.
558 lockmem=siint Pin down the specified amount of memory with mlock(2). Can
559 potentially be used instead of removing memory or booting
560 with less memory to simulate a smaller amount of memory.
562 exec_prerun=str Before running this job, issue the command specified
565 exec_postrun=str After the job completes, issue the command specified
568 ioscheduler=str Attempt to switch the device hosting the file to the specified
569 io scheduler before running.
571 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
572 percentage of CPU cycles.
574 cpuchunks=int If the job is a CPU cycle eater, split the load into
575 cycles of the given time. In milliseconds.
578 6.0 Interpreting the output
579 ---------------------------
581 fio spits out a lot of output. While running, fio will display the
582 status of the jobs created. An example of that would be:
584 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
586 The characters inside the square brackets denote the current status of
587 each thread. The possible values (in typical life cycle order) are:
591 P Thread setup, but not started.
593 I Thread initialized, waiting.
594 R Running, doing sequential reads.
595 r Running, doing random reads.
596 W Running, doing sequential writes.
597 w Running, doing random writes.
598 M Running, doing mixed sequential reads/writes.
599 m Running, doing mixed random reads/writes.
600 F Running, currently waiting for fsync()
601 V Running, doing verification of written data.
602 E Thread exited, not reaped by main thread yet.
605 The other values are fairly self explanatory - number of threads
606 currently running and doing io, rate of io since last check, and the estimated
607 completion percentage and time for the running group. It's impossible to
608 estimate runtime of the following groups (if any).
610 When fio is done (or interrupted by ctrl-c), it will show the data for
611 each thread, group of threads, and disks in that order. For each data
612 direction, the output looks like:
614 Client1 (g=0): err= 0:
615 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
616 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
617 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
618 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
619 cpu : usr=1.49%, sys=0.25%, ctx=7969
620 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
621 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
622 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
624 The client number is printed, along with the group id and error of that
625 thread. Below is the io statistics, here for writes. In the order listed,
628 io= Number of megabytes io performed
629 bw= Average bandwidth rate
630 runt= The runtime of that thread
631 slat= Submission latency (avg being the average, dev being the
632 standard deviation). This is the time it took to submit
633 the io. For sync io, the slat is really the completion
634 latency, since queue/complete is one operation there.
635 clat= Completion latency. Same names as slat, this denotes the
636 time from submission to completion of the io pieces. For
637 sync io, clat will usually be equal (or very close) to 0,
638 as the time from submit to complete is basically just
639 CPU time (io has already been done, see slat explanation).
640 bw= Bandwidth. Same names as the xlat stats, but also includes
641 an approximate percentage of total aggregate bandwidth
642 this thread received in this group. This last value is
643 only really useful if the threads in this group are on the
644 same disk, since they are then competing for disk access.
645 cpu= CPU usage. User and system time, along with the number
646 of context switches this thread went through.
647 IO depths= The distribution of io depths over the job life time. The
648 numbers are divided into powers of 2, so for example the
649 16= entries includes depths up to that value but higher
650 than the previous entry. In other words, it covers the
652 IO latencies= The distribution of IO completion latencies. This is the
653 time from when IO leaves fio and when it gets completed.
654 The numbers follow the same pattern as the IO depths,
655 meaning that 2=1.6% means that 1.6% of the IO completed
656 within 2 msecs, 20=12.8% means that 12.8% of the IO
657 took more than 10 msecs, but less than (or equal to) 20 msecs.
659 After each client has been listed, the group statistics are printed. They
662 Run status group 0 (all jobs):
663 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
664 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
666 For each data direction, it prints:
668 io= Number of megabytes io performed.
669 aggrb= Aggregate bandwidth of threads in this group.
670 minb= The minimum average bandwidth a thread saw.
671 maxb= The maximum average bandwidth a thread saw.
672 mint= The smallest runtime of the threads in that group.
673 maxt= The longest runtime of the threads in that group.
675 And finally, the disk statistics are printed. They will look like this:
677 Disk stats (read/write):
678 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
680 Each value is printed for both reads and writes, with reads first. The
683 ios= Number of ios performed by all groups.
684 merge= Number of merges io the io scheduler.
685 ticks= Number of ticks we kept the disk busy.
686 io_queue= Total time spent in the disk queue.
687 util= The disk utilization. A value of 100% means we kept the disk
688 busy constantly, 50% would be a disk idling half of the time.
694 For scripted usage where you typically want to generate tables or graphs
695 of the results, fio can output the results in a semicolon separated format.
696 The format is one long line of values, such as:
698 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%
699 ;0.0%;0.0%;0.0%;0.0%;0.0%
701 Split up, the format is as follows:
703 jobname, groupid, error
705 KiB IO, bandwidth (KiB/sec), runtime (msec)
706 Submission latency: min, max, mean, deviation
707 Completion latency: min, max, mean, deviation
708 Bw: min, max, aggregate percentage of total, mean, deviation
710 KiB IO, bandwidth (KiB/sec), runtime (msec)
711 Submission latency: min, max, mean, deviation
712 Completion latency: min, max, mean, deviation
713 Bw: min, max, aggregate percentage of total, mean, deviation
714 CPU usage: user, system, context switches
715 IO depths: <=1, 2, 4, 8, 16, 32, >=64
716 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000