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.
210 rw=str Type of io pattern. Accepted values are:
212 read Sequential reads
213 write Sequential writes
214 randwrite Random writes
215 randread Random reads
216 rw Sequential mixed reads and writes
217 randrw Random mixed reads and writes
219 For the mixed io types, the default is to split them 50/50.
220 For certain types of io the result may still be skewed a bit,
221 since the speed may be different.
223 randrepeat=bool For random IO workloads, seed the generator in a predictable
224 way so that results are repeatable across repetitions.
226 size=siint The total size of file io for this job. This may describe
227 the size of the single file the job uses, or it may be
228 divided between the number of files in the job. If the
229 file already exists, the file size will be adjusted to this
230 size if larger than the current file size. If this parameter
231 is not given and the file exists, the file size will be used.
233 bs=siint The block size used for the io units. Defaults to 4k. Values
234 can be given for both read and writes. If a single siint is
235 given, it will apply to both. If a second siint is specified
236 after a comma, it will apply to writes only. In other words,
237 the format is either bs=read_and_write or bs=read,write.
238 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
239 for writes. If you only wish to set the write size, you
240 can do so by passing an empty read size - bs=,8k will set
241 8k for writes and leave the read default value.
243 bsrange=irange Instead of giving a single block size, specify a range
244 and fio will mix the issued io block sizes. The issued
245 io unit will always be a multiple of the minimum value
246 given (also see bs_unaligned). Applies to both reads and
247 writes, however a second range can be given after a comma.
250 bs_unaligned If this option is given, any byte size value within bsrange
251 may be used as a block range. This typically wont work with
252 direct IO, as that normally requires sector alignment.
254 nrfiles=int Number of files to use for this job. Defaults to 1.
256 openfiles=int Number of files to keep open at the same time. Defaults to
257 the same as nrfiles, can be set smaller to limit the number
260 file_service_type=str Defines how fio decides which file from a job to
261 service next. The following types are defined:
263 random Just choose a file at random.
265 roundrobin Round robin over open files. This
268 ioengine=str Defines how the job issues io to the file. The following
271 sync Basic read(2) or write(2) io. lseek(2) is
272 used to position the io location.
274 libaio Linux native asynchronous io.
276 posixaio glibc posix asynchronous io.
278 mmap File is memory mapped and data copied
279 to/from using memcpy(3).
281 splice splice(2) is used to transfer the data and
282 vmsplice(2) to transfer data from user
285 syslet-rw Use the syslet system calls to make
286 regular read/write async.
288 sg SCSI generic sg v3 io. May either be
289 synchronous using the SG_IO ioctl, or if
290 the target is an sg character device
291 we use read(2) and write(2) for asynchronous
294 null Doesn't transfer any data, just pretends
295 to. This is mainly used to exercise fio
296 itself and for debugging/testing purposes.
298 net Transfer over the network to given host:port.
299 'filename' must be set appropriately to
300 filename=host:port regardless of send
301 or receive, if the latter only the port
304 cpu Doesn't transfer any data, but burns CPU
305 cycles according to the cpuload= and
306 cpucycle= options. Setting cpuload=85
307 will cause that job to do nothing but burn
310 external Prefix to specify loading an external
311 IO engine object file. Append the engine
312 filename, eg ioengine=external:/tmp/foo.o
313 to load ioengine foo.o in /tmp.
315 iodepth=int This defines how many io units to keep in flight against
316 the file. The default is 1 for each file defined in this
317 job, can be overridden with a larger value for higher
320 iodepth_batch=int This defines how many pieces of IO to submit at once.
321 It defaults to the same as iodepth, but can be set lower
324 iodepth_low=int The low water mark indicating when to start filling
325 the queue again. Defaults to the same as iodepth, meaning
326 that fio will attempt to keep the queue full at all times.
327 If iodepth is set to eg 16 and iodepth_low is set to 4, then
328 after fio has filled the queue of 16 requests, it will let
329 the depth drain down to 4 before starting to fill it again.
331 direct=bool If value is true, use non-buffered io. This is usually
334 buffered=bool If value is true, use buffered io. This is the opposite
335 of the 'direct' option. Defaults to true.
337 offset=siint Start io at the given offset in the file. The data before
338 the given offset will not be touched. This effectively
339 caps the file size at real_size - offset.
341 fsync=int If writing to a file, issue a sync of the dirty data
342 for every number of blocks given. For example, if you give
343 32 as a parameter, fio will sync the file for every 32
344 writes issued. If fio is using non-buffered io, we may
345 not sync the file. The exception is the sg io engine, which
346 synchronizes the disk cache anyway.
348 overwrite=bool If writing to a file, setup the file first and do overwrites.
350 end_fsync=bool If true, fsync file contents when the job exits.
352 rwmixcycle=int Value in milliseconds describing how often to switch between
353 reads and writes for a mixed workload. The default is
356 rwmixread=int How large a percentage of the mix should be reads.
358 rwmixwrite=int How large a percentage of the mix should be writes. If both
359 rwmixread and rwmixwrite is given and the values do not add
360 up to 100%, the latter of the two will be used to override
363 norandommap Normally fio will cover every block of the file when doing
364 random IO. If this option is given, fio will just get a
365 new random offset without looking at past io history. This
366 means that some blocks may not be read or written, and that
367 some blocks may be read/written more than once. This option
368 is mutually exclusive with verify= for that reason.
370 nice=int Run the job with the given nice value. See man nice(2).
372 prio=int Set the io priority value of this job. Linux limits us to
373 a positive value between 0 and 7, with 0 being the highest.
376 prioclass=int Set the io priority class. See man ionice(1).
378 thinktime=int Stall the job x microseconds after an io has completed before
379 issuing the next. May be used to simulate processing being
380 done by an application. See thinktime_blocks and
384 Only valid if thinktime is set - pretend to spend CPU time
385 doing something with the data received, before falling back
386 to sleeping for the rest of the period specified by
390 Only valid if thinktime is set - control how many blocks
391 to issue, before waiting 'thinktime' usecs. If not set,
392 defaults to 1 which will make fio wait 'thinktime' usecs
395 rate=int Cap the bandwidth used by this job to this number of KiB/sec.
397 ratemin=int Tell fio to do whatever it can to maintain at least this
400 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
403 cpumask=int Set the CPU affinity of this job. The parameter given is a
404 bitmask of allowed CPU's the job may run on. See man
405 sched_setaffinity(2).
407 startdelay=int Start this job the specified number of seconds after fio
408 has started. Only useful if the job file contains several
409 jobs, and you want to delay starting some jobs to a certain
412 runtime=int Tell fio to terminate processing after the specified number
413 of seconds. It can be quite hard to determine for how long
414 a specified job will run, so this parameter is handy to
415 cap the total runtime to a given time.
417 invalidate=bool Invalidate the buffer/page cache parts for this file prior
418 to starting io. Defaults to true.
420 sync=bool Use sync io for buffered writes. For the majority of the
421 io engines, this means using O_SYNC.
423 mem=str Fio can use various types of memory as the io unit buffer.
424 The allowed values are:
426 malloc Use memory from malloc(3) as the buffers.
428 shm Use shared memory as the buffers. Allocated
431 shmhuge Same as shm, but use huge pages as backing.
433 mmap Use mmap to allocate buffers. May either be
434 anonymous memory, or can be file backed if
435 a filename is given after the option. The
436 format is mem=mmap:/path/to/file.
438 mmaphuge Use a memory mapped huge file as the buffer
439 backing. Append filename after mmaphuge, ala
440 mem=mmaphuge:/hugetlbfs/file
442 The area allocated is a function of the maximum allowed
443 bs size for the job, multiplied by the io depth given. Note
444 that for shmhuge and mmaphuge to work, the system must have
445 free huge pages allocated. This can normally be checked
446 and set by reading/writing /proc/sys/vm/nr_hugepages on a
447 Linux system. Fio assumes a huge page is 4MiB in size. So
448 to calculate the number of huge pages you need for a given
449 job file, add up the io depth of all jobs (normally one unless
450 iodepth= is used) and multiply by the maximum bs set. Then
451 divide that number by the huge page size. You can see the
452 size of the huge pages in /proc/meminfo. If no huge pages
453 are allocated by having a non-zero number in nr_hugepages,
454 using mmaphuge or shmhuge will fail. Also see hugepage-size.
456 mmaphuge also needs to have hugetlbfs mounted and the file
457 location should point there. So if it's mounted in /huge,
458 you would use mem=mmaphuge:/huge/somefile.
461 Defines the size of a huge page. Must at least be equal
462 to the system setting, see /proc/meminfo. Defaults to 4MiB.
463 Should probably always be a multiple of megabytes, so using
464 hugepage-size=Xm is the preferred way to set this to avoid
465 setting a non-pow-2 bad value.
467 exitall When one job finishes, terminate the rest. The default is
468 to wait for each job to finish, sometimes that is not the
471 bwavgtime=int Average the calculated bandwidth over the given time. Value
472 is specified in milliseconds.
474 create_serialize=bool If true, serialize the file creating for the jobs.
475 This may be handy to avoid interleaving of data
476 files, which may greatly depend on the filesystem
477 used and even the number of processors in the system.
479 create_fsync=bool fsync the data file after creation. This is the
482 unlink=bool Unlink the job files when done. Not the default, as repeated
483 runs of that job would then waste time recreating the fileset
486 loops=int Run the specified number of iterations of this job. Used
487 to repeat the same workload a given number of times. Defaults
490 verify=str If writing to a file, fio can verify the file contents
491 after each iteration of the job. The allowed values are:
493 md5 Use an md5 sum of the data area and store
494 it in the header of each block.
496 crc32 Use a crc32 sum of the data area and store
497 it in the header of each block.
499 This option can be used for repeated burn-in tests of a
500 system to make sure that the written data is also
503 stonewall Wait for preceeding jobs in the job file to exit, before
504 starting this one. Can be used to insert serialization
505 points in the job file.
507 numjobs=int Create the specified number of clones of this job. May be
508 used to setup a larger number of threads/processes doing
509 the same thing. We regard that grouping of jobs as a
512 group_reporting If 'numjobs' is set, it may be interesting to display
513 statistics for the group as a whole instead of for each
514 individual job. This is especially true of 'numjobs' is
515 large, looking at individual thread/process output quickly
516 becomes unwieldy. If 'group_reporting' is specified, fio
517 will show the final report per-group instead of per-job.
519 thread fio defaults to forking jobs, however if this option is
520 given, fio will use pthread_create(3) to create threads
523 zonesize=siint Divide a file into zones of the specified size. See zoneskip.
525 zoneskip=siint Skip the specified number of bytes when zonesize data has
526 been read. The two zone options can be used to only do
527 io on zones of a file.
529 write_iolog=str Write the issued io patterns to the specified file. See
532 read_iolog=str Open an iolog with the specified file name and replay the
533 io patterns it contains. This can be used to store a
534 workload and replay it sometime later.
536 write_bw_log If given, write a bandwidth log of the jobs in this job
537 file. Can be used to store data of the bandwidth of the
538 jobs in their lifetime. The included fio_generate_plots
539 script uses gnuplot to turn these text files into nice
542 write_lat_log Same as write_bw_log, except that this option stores io
543 completion latencies instead.
545 lockmem=siint Pin down the specified amount of memory with mlock(2). Can
546 potentially be used instead of removing memory or booting
547 with less memory to simulate a smaller amount of memory.
549 exec_prerun=str Before running this job, issue the command specified
552 exec_postrun=str After the job completes, issue the command specified
555 ioscheduler=str Attempt to switch the device hosting the file to the specified
556 io scheduler before running.
558 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
559 percentage of CPU cycles.
561 cpuchunks=int If the job is a CPU cycle eater, split the load into
562 cycles of the given time. In milliseconds.
565 6.0 Interpreting the output
566 ---------------------------
568 fio spits out a lot of output. While running, fio will display the
569 status of the jobs created. An example of that would be:
571 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
573 The characters inside the square brackets denote the current status of
574 each thread. The possible values (in typical life cycle order) are:
578 P Thread setup, but not started.
580 I Thread initialized, waiting.
581 R Running, doing sequential reads.
582 r Running, doing random reads.
583 W Running, doing sequential writes.
584 w Running, doing random writes.
585 M Running, doing mixed sequential reads/writes.
586 m Running, doing mixed random reads/writes.
587 F Running, currently waiting for fsync()
588 V Running, doing verification of written data.
589 E Thread exited, not reaped by main thread yet.
592 The other values are fairly self explanatory - number of threads
593 currently running and doing io, rate of io since last check, and the estimated
594 completion percentage and time for the running group. It's impossible to
595 estimate runtime of the following groups (if any).
597 When fio is done (or interrupted by ctrl-c), it will show the data for
598 each thread, group of threads, and disks in that order. For each data
599 direction, the output looks like:
601 Client1 (g=0): err= 0:
602 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
603 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
604 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
605 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
606 cpu : usr=1.49%, sys=0.25%, ctx=7969
607 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
608 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
609 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
611 The client number is printed, along with the group id and error of that
612 thread. Below is the io statistics, here for writes. In the order listed,
615 io= Number of megabytes io performed
616 bw= Average bandwidth rate
617 runt= The runtime of that thread
618 slat= Submission latency (avg being the average, dev being the
619 standard deviation). This is the time it took to submit
620 the io. For sync io, the slat is really the completion
621 latency, since queue/complete is one operation there.
622 clat= Completion latency. Same names as slat, this denotes the
623 time from submission to completion of the io pieces. For
624 sync io, clat will usually be equal (or very close) to 0,
625 as the time from submit to complete is basically just
626 CPU time (io has already been done, see slat explanation).
627 bw= Bandwidth. Same names as the xlat stats, but also includes
628 an approximate percentage of total aggregate bandwidth
629 this thread received in this group. This last value is
630 only really useful if the threads in this group are on the
631 same disk, since they are then competing for disk access.
632 cpu= CPU usage. User and system time, along with the number
633 of context switches this thread went through.
634 IO depths= The distribution of io depths over the job life time. The
635 numbers are divided into powers of 2, so for example the
636 16= entries includes depths up to that value but higher
637 than the previous entry. In other words, it covers the
639 IO latencies= The distribution of IO completion latencies. This is the
640 time from when IO leaves fio and when it gets completed.
641 The numbers follow the same pattern as the IO depths,
642 meaning that 2=1.6% means that 1.6% of the IO completed
643 within 2 msecs, 20=12.8% means that 12.8% of the IO
644 took more than 10 msecs, but less than (or equal to) 20 msecs.
646 After each client has been listed, the group statistics are printed. They
649 Run status group 0 (all jobs):
650 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
651 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
653 For each data direction, it prints:
655 io= Number of megabytes io performed.
656 aggrb= Aggregate bandwidth of threads in this group.
657 minb= The minimum average bandwidth a thread saw.
658 maxb= The maximum average bandwidth a thread saw.
659 mint= The smallest runtime of the threads in that group.
660 maxt= The longest runtime of the threads in that group.
662 And finally, the disk statistics are printed. They will look like this:
664 Disk stats (read/write):
665 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
667 Each value is printed for both reads and writes, with reads first. The
670 ios= Number of ios performed by all groups.
671 merge= Number of merges io the io scheduler.
672 ticks= Number of ticks we kept the disk busy.
673 io_queue= Total time spent in the disk queue.
674 util= The disk utilization. A value of 100% means we kept the disk
675 busy constantly, 50% would be a disk idling half of the time.
681 For scripted usage where you typically want to generate tables or graphs
682 of the results, fio can output the results in a semicolon separated format.
683 The format is one long line of values, such as:
685 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%
686 ;0.0%;0.0%;0.0%;0.0%;0.0%
688 Split up, the format is as follows:
690 jobname, groupid, error
692 KiB IO, bandwidth (KiB/sec), runtime (msec)
693 Submission latency: min, max, mean, deviation
694 Completion latency: min, max, mean, deviation
695 Bw: min, max, aggregate percentage of total, mean, deviation
697 KiB IO, bandwidth (KiB/sec), runtime (msec)
698 Submission latency: min, max, mean, deviation
699 Completion latency: min, max, mean, deviation
700 Bw: min, max, aggregate percentage of total, mean, deviation
701 CPU usage: user, system, context switches
702 IO depths: <=1, 2, 4, 8, 16, 32, >=64
703 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000