[PATCH] Simple support for networked IO
[fio.git] / HOWTO
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1Table of contents
2-----------------
3
41. Overview
52. How fio works
63. Running fio
74. Job file format
85. Detailed list of parameters
96. Normal output
107. Terse output
11
12
131.0 Overview and history
14------------------------
15fio was originally written to save me the hassle of writing special test
16case programs when I wanted to test a specific workload, either for
17performance reasons or to find/reproduce a bug. The process of writing
18such a test app can be tiresome, especially if you have to do it often.
19Hence I needed a tool that would be able to simulate a given io workload
20without resorting to writing a tailored test case again and again.
21
22A test work load is difficult to define, though. There can be any number
23of processes or threads involved, and they can each be using their own
24way of generating io. You could have someone dirtying large amounts of
25memory in an memory mapped file, or maybe several threads issuing
26reads using asynchronous io. fio needed to be flexible enough to
27simulate both of these cases, and many more.
28
292.0 How fio works
30-----------------
31The first step in getting fio to simulate a desired io workload, is
32writing a job file describing that specific setup. A job file may contain
33any number of threads and/or files - the typical contents of the job file
34is a global section defining shared parameters, and one or more job
35sections describing the jobs involved. When run, fio parses this file
36and sets everything up as described. If we break down a job from top to
37bottom, it contains the following basic parameters:
38
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.
43
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
46 block sizes.
47
48 IO size How much data are we going to be reading/writing.
49
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, or even
53 SG (SCSI generic sg).
54
6c219763 55 IO depth If the io engine is async, how large a queuing
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56 depth do we want to maintain?
57
58 IO type Should we be doing buffered io, or direct/raw io?
59
60 Num files How many files are we spreading the workload over.
61
62 Num threads How many threads or processes should we spread
63 this workload over.
64
65The above are the basic parameters defined for a workload, in addition
66there's a multitude of parameters that modify other aspects of how this
67job behaves.
68
69
703.0 Running fio
71---------------
72See the README file for command line parameters, there are only a few
73of them.
74
75Running fio is normally the easiest part - you just give it the job file
76(or job files) as parameters:
77
78$ fio job_file
79
80and it will start doing what the job_file tells it to do. You can give
81more than one job file on the command line, fio will serialize the running
82of those files. Internally that is the same as using the 'stonewall'
83parameter described the the parameter section.
84
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85If the job file contains only one job, you may as well just give the
86parameters on the command line. The command line parameters are identical
87to the job parameters, with a few extra that control global parameters
88(see README). For example, for the job file parameter iodepth=2, the
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89mirror command line option would be --iodepth 2 or --iodepth=2. You can
90also 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.
92Command line entries following a --name entry will apply to that job,
93until there are no more entries or a new --name entry is seen. This is
94similar to the job file options, where each option applies to the current
95job until a new [] job entry is seen.
b4692828 96
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97fio does not need to run as root, except if the files or devices specified
98in the job section requires that. Some other options may also be restricted,
6c219763 99such as memory locking, io scheduler switching, and decreasing the nice value.
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100
101
1024.0 Job file format
103-------------------
104As previously described, fio accepts one or more job files describing
105what it is supposed to do. The job file format is the classic ini file,
106where the names enclosed in [] brackets define the job name. You are free
107to use any ascii name you want, except 'global' which has special meaning.
108A global section sets defaults for the jobs described in that file. A job
109may override a global section parameter, and a job file may even have
110several global sections if so desired. A job is only affected by a global
111section residing above it. If the first character in a line is a ';', the
112entire line is discarded as a comment.
113
114So lets look at a really simple job file that define to threads, each
115randomly reading from a 128MiB file.
116
117; -- start job file --
118[global]
119rw=randread
120size=128m
121
122[job1]
123
124[job2]
125
126; -- end job file --
127
128As you can see, the job file sections themselves are empty as all the
129described parameters are shared. As no filename= option is given, fio
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130makes up a filename for each of the jobs as it sees fit. On the command
131line, this job would look as follows:
132
133$ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
134
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135
136Lets look at an example that have a number of processes writing randomly
137to files.
138
139; -- start job file --
140[random-writers]
141ioengine=libaio
142iodepth=4
143rw=randwrite
144bs=32k
145direct=0
146size=64m
147numjobs=4
148
149; -- end job file --
150
151Here we have no global section, as we only have one job defined anyway.
152We want to use async io here, with a depth of 4 for each file. We also
153increased the buffer size used to 32KiB and define numjobs to 4 to
154fork 4 identical jobs. The result is 4 processes each randomly writing
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155to their own 64MiB file. Instead of using the above job file, you could
156have given the parameters on the command line. For this case, you would
157specify:
158
159$ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
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160
161fio ships with a few example job files, you can also look there for
162inspiration.
163
164
1655.0 Detailed list of parameters
166-------------------------------
167
168This section describes in details each parameter associated with a job.
169Some parameters take an option of a given type, such as an integer or
170a string. The following types are used:
171
172str String. This is a sequence of alpha characters.
173int Integer. A whole number value, may be negative.
174siint SI integer. A whole number value, which may contain a postfix
175 describing the base of the number. Accepted postfixes are k/m/g,
6c219763 176 meaning kilo, mega, and giga. So if you want to specify 4096,
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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.
179bool Boolean. Usually parsed as an integer, however only defined for
180 true and false (1 and 0).
181irange Integer range with postfix. Allows value range to be given, such
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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
185 siint.
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186
187With the above in mind, here follows the complete list of fio job
188parameters.
189
190name=str ASCII name of the job. This may be used to override the
191 name printed by fio for this job. Otherwise the job
c2b1e753 192 name is used. On the command line this parameter has the
6c219763 193 special purpose of also signaling the start of a new
c2b1e753 194 job.
71bfa161 195
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196description=str Text description of the job. Doesn't do anything except
197 dump this text description when this job is run. It's
198 not parsed.
199
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200directory=str Prefix filenames with this directory. Used to places files
201 in a different location than "./".
202
203filename=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
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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.
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209
210rw=str Type of io pattern. Accepted values are:
211
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
218
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.
222
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223randrepeat=bool For random IO workloads, seed the generator in a predictable
224 way so that results are repeatable across repetitions.
225
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226size=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.
232
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233bs=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
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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.
a00735e6 242
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243bsrange=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
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246 given (also see bs_unaligned). Applies to both reads and
247 writes, however a second range can be given after a comma.
248 See bs=.
a00735e6 249
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250bs_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.
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253
254nrfiles=int Number of files to use for this job. Defaults to 1.
255
256ioengine=str Defines how the job issues io to the file. The following
257 types are defined:
258
259 sync Basic read(2) or write(2) io. lseek(2) is
260 used to position the io location.
261
262 libaio Linux native asynchronous io.
263
264 posixaio glibc posix asynchronous io.
265
266 mmap File is memory mapped and data copied
267 to/from using memcpy(3).
268
269 splice splice(2) is used to transfer the data and
270 vmsplice(2) to transfer data from user
271 space to the kernel.
272
273 sg SCSI generic sg v3 io. May either be
6c219763 274 synchronous using the SG_IO ioctl, or if
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275 the target is an sg character device
276 we use read(2) and write(2) for asynchronous
277 io.
278
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279 null Doesn't transfer any data, just pretends
280 to. This is mainly used to exercise fio
281 itself and for debugging/testing purposes.
282
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283 net Transfer over the network to given host:port.
284 'filename' must be set appropriately to
285 filename=host:port regardless of send
286 or receive, if the latter only the port
287 argument is used.
288
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289iodepth=int This defines how many io units to keep in flight against
290 the file. The default is 1 for each file defined in this
291 job, can be overridden with a larger value for higher
292 concurrency.
293
294direct=bool If value is true, use non-buffered io. This is usually
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295 O_DIRECT.
296
297buffered=bool If value is true, use buffered io. This is the opposite
298 of the 'direct' option. Defaults to true.
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299
300offset=siint Start io at the given offset in the file. The data before
301 the given offset will not be touched. This effectively
302 caps the file size at real_size - offset.
303
304fsync=int If writing to a file, issue a sync of the dirty data
305 for every number of blocks given. For example, if you give
306 32 as a parameter, fio will sync the file for every 32
307 writes issued. If fio is using non-buffered io, we may
308 not sync the file. The exception is the sg io engine, which
6c219763 309 synchronizes the disk cache anyway.
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310
311overwrite=bool If writing to a file, setup the file first and do overwrites.
312
313end_fsync=bool If true, fsync file contents when the job exits.
314
6c219763 315rwmixcycle=int Value in milliseconds describing how often to switch between
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316 reads and writes for a mixed workload. The default is
317 500 msecs.
318
319rwmixread=int How large a percentage of the mix should be reads.
320
321rwmixwrite=int How large a percentage of the mix should be writes. If both
322 rwmixread and rwmixwrite is given and the values do not add
323 up to 100%, the latter of the two will be used to override
324 the first.
325
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326norandommap Normally fio will cover every block of the file when doing
327 random IO. If this option is given, fio will just get a
328 new random offset without looking at past io history. This
329 means that some blocks may not be read or written, and that
330 some blocks may be read/written more than once. This option
331 is mutually exclusive with verify= for that reason.
332
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333nice=int Run the job with the given nice value. See man nice(2).
334
335prio=int Set the io priority value of this job. Linux limits us to
336 a positive value between 0 and 7, with 0 being the highest.
337 See man ionice(1).
338
339prioclass=int Set the io priority class. See man ionice(1).
340
341thinktime=int Stall the job x microseconds after an io has completed before
342 issuing the next. May be used to simulate processing being
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343 done by an application. See thinktime_blocks.
344
345thinktime_blocks
346 Only valid if thinktime is set - control how many blocks
347 to issue, before waiting 'thinktime' usecs. If not set,
348 defaults to 1 which will make fio wait 'thinktime' usecs
349 after every block.
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350
351rate=int Cap the bandwidth used by this job to this number of KiB/sec.
352
353ratemin=int Tell fio to do whatever it can to maintain at least this
354 bandwidth.
355
356ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
6c219763 357 of milliseconds.
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358
359cpumask=int Set the CPU affinity of this job. The parameter given is a
360 bitmask of allowed CPU's the job may run on. See man
361 sched_setaffinity(2).
362
363startdelay=int Start this job the specified number of seconds after fio
364 has started. Only useful if the job file contains several
365 jobs, and you want to delay starting some jobs to a certain
366 time.
367
03b74b3e 368runtime=int Tell fio to terminate processing after the specified number
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369 of seconds. It can be quite hard to determine for how long
370 a specified job will run, so this parameter is handy to
371 cap the total runtime to a given time.
372
373invalidate=bool Invalidate the buffer/page cache parts for this file prior
374 to starting io. Defaults to true.
375
376sync=bool Use sync io for buffered writes. For the majority of the
377 io engines, this means using O_SYNC.
378
379mem=str Fio can use various types of memory as the io unit buffer.
380 The allowed values are:
381
382 malloc Use memory from malloc(3) as the buffers.
383
384 shm Use shared memory as the buffers. Allocated
385 through shmget(2).
386
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387 shmhuge Same as shm, but use huge pages as backing.
388
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389 mmap Use mmap to allocate buffers. May either be
390 anonymous memory, or can be file backed if
391 a filename is given after the option. The
392 format is mem=mmap:/path/to/file.
71bfa161 393
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394 mmaphuge Use a memory mapped huge file as the buffer
395 backing. Append filename after mmaphuge, ala
396 mem=mmaphuge:/hugetlbfs/file
397
71bfa161 398 The area allocated is a function of the maximum allowed
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399 bs size for the job, multiplied by the io depth given. Note
400 that for shmhuge and mmaphuge to work, the system must have
401 free huge pages allocated. This can normally be checked
402 and set by reading/writing /proc/sys/vm/nr_hugepages on a
403 Linux system. Fio assumes a huge page is 4MiB in size. So
404 to calculate the number of huge pages you need for a given
405 job file, add up the io depth of all jobs (normally one unless
406 iodepth= is used) and multiply by the maximum bs set. Then
407 divide that number by the huge page size. You can see the
408 size of the huge pages in /proc/meminfo. If no huge pages
409 are allocated by having a non-zero number in nr_hugepages,
56bb17f2 410 using mmaphuge or shmhuge will fail. Also see hugepage-size.
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411
412 mmaphuge also needs to have hugetlbfs mounted and the file
413 location should point there. So if it's mounted in /huge,
414 you would use mem=mmaphuge:/huge/somefile.
71bfa161 415
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416hugepage-size=siint
417 Defines the size of a huge page. Must at least be equal
418 to the system setting, see /proc/meminfo. Defaults to 4MiB.
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419 Should probably always be a multiple of megabytes, so using
420 hugepage-size=Xm is the preferred way to set this to avoid
421 setting a non-pow-2 bad value.
56bb17f2 422
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423exitall When one job finishes, terminate the rest. The default is
424 to wait for each job to finish, sometimes that is not the
425 desired action.
426
427bwavgtime=int Average the calculated bandwidth over the given time. Value
6c219763 428 is specified in milliseconds.
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429
430create_serialize=bool If true, serialize the file creating for the jobs.
431 This may be handy to avoid interleaving of data
432 files, which may greatly depend on the filesystem
433 used and even the number of processors in the system.
434
435create_fsync=bool fsync the data file after creation. This is the
436 default.
437
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438unlink=bool Unlink the job files when done. Not the default, as repeated
439 runs of that job would then waste time recreating the fileset
440 again and again.
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441
442loops=int Run the specified number of iterations of this job. Used
443 to repeat the same workload a given number of times. Defaults
444 to 1.
445
446verify=str If writing to a file, fio can verify the file contents
447 after each iteration of the job. The allowed values are:
448
449 md5 Use an md5 sum of the data area and store
450 it in the header of each block.
451
452 crc32 Use a crc32 sum of the data area and store
453 it in the header of each block.
454
6c219763 455 This option can be used for repeated burn-in tests of a
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456 system to make sure that the written data is also
457 correctly read back.
458
459stonewall Wait for preceeding jobs in the job file to exit, before
460 starting this one. Can be used to insert serialization
461 points in the job file.
462
463numjobs=int Create the specified number of clones of this job. May be
464 used to setup a larger number of threads/processes doing
465 the same thing.
466
467thread fio defaults to forking jobs, however if this option is
468 given, fio will use pthread_create(3) to create threads
469 instead.
470
471zonesize=siint Divide a file into zones of the specified size. See zoneskip.
472
473zoneskip=siint Skip the specified number of bytes when zonesize data has
474 been read. The two zone options can be used to only do
475 io on zones of a file.
476
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477write_iolog=str Write the issued io patterns to the specified file. See
478 read_iolog.
71bfa161 479
076efc7c 480read_iolog=str Open an iolog with the specified file name and replay the
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481 io patterns it contains. This can be used to store a
482 workload and replay it sometime later.
483
484write_bw_log If given, write a bandwidth log of the jobs in this job
485 file. Can be used to store data of the bandwidth of the
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486 jobs in their lifetime. The included fio_generate_plots
487 script uses gnuplot to turn these text files into nice
488 graphs.
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489
490write_lat_log Same as write_bw_log, except that this option stores io
491 completion latencies instead.
492
493lockmem=siint Pin down the specified amount of memory with mlock(2). Can
494 potentially be used instead of removing memory or booting
495 with less memory to simulate a smaller amount of memory.
496
497exec_prerun=str Before running this job, issue the command specified
498 through system(3).
499
500exec_postrun=str After the job completes, issue the command specified
501 though system(3).
502
503ioscheduler=str Attempt to switch the device hosting the file to the specified
504 io scheduler before running.
505
506cpuload=int If the job is a CPU cycle eater, attempt to use the specified
507 percentage of CPU cycles.
508
509cpuchunks=int If the job is a CPU cycle eater, split the load into
6c219763 510 cycles of the given time. In milliseconds.
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511
512
5136.0 Interpreting the output
514---------------------------
515
516fio spits out a lot of output. While running, fio will display the
517status of the jobs created. An example of that would be:
518
73c8b082 519Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
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520
521The characters inside the square brackets denote the current status of
522each thread. The possible values (in typical life cycle order) are:
523
524Idle Run
525---- ---
526P Thread setup, but not started.
527C Thread created.
528I Thread initialized, waiting.
529 R Running, doing sequential reads.
530 r Running, doing random reads.
531 W Running, doing sequential writes.
532 w Running, doing random writes.
533 M Running, doing mixed sequential reads/writes.
534 m Running, doing mixed random reads/writes.
535 F Running, currently waiting for fsync()
536V Running, doing verification of written data.
537E Thread exited, not reaped by main thread yet.
538_ Thread reaped.
539
540The other values are fairly self explanatory - number of threads
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541currently running and doing io, rate of io since last check, and the estimated
542completion percentage and time for the running group. It's impossible to
543estimate runtime of the following groups (if any).
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544
545When fio is done (or interrupted by ctrl-c), it will show the data for
546each thread, group of threads, and disks in that order. For each data
547direction, the output looks like:
548
549Client1 (g=0): err= 0:
550 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
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551 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
552 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
553 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
71bfa161 554 cpu : usr=1.49%, sys=0.25%, ctx=7969
71619dc2 555 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
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556
557The client number is printed, along with the group id and error of that
558thread. Below is the io statistics, here for writes. In the order listed,
559they denote:
560
561io= Number of megabytes io performed
562bw= Average bandwidth rate
563runt= The runtime of that thread
564 slat= Submission latency (avg being the average, dev being the
565 standard deviation). This is the time it took to submit
566 the io. For sync io, the slat is really the completion
567 latency, since queue/complete is one operation there.
568 clat= Completion latency. Same names as slat, this denotes the
569 time from submission to completion of the io pieces. For
570 sync io, clat will usually be equal (or very close) to 0,
571 as the time from submit to complete is basically just
572 CPU time (io has already been done, see slat explanation).
573 bw= Bandwidth. Same names as the xlat stats, but also includes
574 an approximate percentage of total aggregate bandwidth
575 this thread received in this group. This last value is
576 only really useful if the threads in this group are on the
577 same disk, since they are then competing for disk access.
578cpu= CPU usage. User and system time, along with the number
579 of context switches this thread went through.
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580IO depths= The distribution of io depths over the job life time. The
581 numbers are divided into powers of 2, so for example the
582 16= entries includes depths up to that value but higher
583 than the previous entry. In other words, it covers the
584 range from 16 to 31.
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585
586After each client has been listed, the group statistics are printed. They
587will look like this:
588
589Run status group 0 (all jobs):
590 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
591 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
592
593For each data direction, it prints:
594
595io= Number of megabytes io performed.
596aggrb= Aggregate bandwidth of threads in this group.
597minb= The minimum average bandwidth a thread saw.
598maxb= The maximum average bandwidth a thread saw.
599mint= The smallest runtime of the threads in that group.
600maxt= The longest runtime of the threads in that group.
601
602And finally, the disk statistics are printed. They will look like this:
603
604Disk stats (read/write):
605 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
606
607Each value is printed for both reads and writes, with reads first. The
608numbers denote:
609
610ios= Number of ios performed by all groups.
611merge= Number of merges io the io scheduler.
612ticks= Number of ticks we kept the disk busy.
613io_queue= Total time spent in the disk queue.
614util= The disk utilization. A value of 100% means we kept the disk
615 busy constantly, 50% would be a disk idling half of the time.
616
617
6187.0 Terse output
619----------------
620
621For scripted usage where you typically want to generate tables or graphs
6c219763 622of the results, fio can output the results in a comma separated format.
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623The format is one long line of values, such as:
624
625client1,0,0,936,331,2894,0,0,0.000000,0.000000,1,170,22.115385,34.290410,16,714,84.252874%,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
626
627Split up, the format is as follows:
628
629 jobname, groupid, error
630 READ status:
631 KiB IO, bandwidth (KiB/sec), runtime (msec)
632 Submission latency: min, max, mean, deviation
633 Completion latency: min, max, mean, deviation
6c219763 634 Bw: min, max, aggregate percentage of total, mean, deviation
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635 WRITE status:
636 KiB IO, bandwidth (KiB/sec), runtime (msec)
637 Submission latency: min, max, mean, deviation
638 Completion latency: min, max, mean, deviation
6c219763 639 Bw: min, max, aggregate percentage of total, mean, deviation
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640 CPU usage: user, system, context switches
641