[PATCH] Support for specifying exact io pattern

[fio.git] / README

fio
---

fio is a tool that will spawn a number of thread doing a particular
type of io action as specified by the user. fio takes a number of
global parameters, each inherited by the thread unless otherwise
parameters given to them overriding that setting is given.


Source
------

fio resides in a git repo, the canonical place is:

git://brick.kernel.dk/data/git/fio.git

Snapshots are frequently generated as well and they include the git
meta data as well. You can download them here:

http://brick.kernel.dk/snaps/


Options
-------

$ fio
	-s IO is sequential
	-b block size in KiB for each io
	-t <sec> Runtime in seconds
	-r For random io, sequence must be repeatable
	-R <on> If one thread fails to meet rate, quit all
	-o <on> Use direct IO is 1, buffered if 0
	-l Generate per-job latency logs
	-w Generate per-job bandwidth logs
	-f <file> Read <file> for job descriptions
	-h Print help info
	-v Print version information and exit

The <jobs> format is as follows:

	directory=x	Use 'x' as the top level directory for storing files
	rw=x		'x' may be: read, randread, write, randwrite,
			rw (read-write mix), randrw (read-write random mix)
	size=x		Set file size to x bytes (x string can include k/m/g)
	ioengine=x	'x' may be: aio/libaio/linuxaio for Linux aio,
			posixaio for POSIX aio, sync for regular read/write io,
			mmap for mmap'ed io, or sgio for direct SG_IO io. The
			latter only works on Linux on SCSI (or SCSI-like
			devices, such as usb-storage or sata/libata driven)
			devices.
	iodepth=x	For async io, allow 'x' ios in flight
	overwrite=x	If 'x', layout a write file first.
	prio=x		Run io at prio X, 0-7 is the kernel allowed range
	prioclass=x	Run io at prio class X
	bs=x		Use 'x' for thread blocksize. May include k/m postfix.
	bsrange=x-y	Mix thread block sizes randomly between x and y. May
			also include k/m postfix.
	direct=x	1 for direct IO, 0 for buffered IO
	thinktime=x	"Think" x usec after each io
	rate=x		Throttle rate to x KiB/sec
	ratemin=x	Quit if rate of x KiB/sec can't be met
	ratecycle=x	ratemin averaged over x msecs
	cpumask=x	Only allow job to run on CPUs defined by mask.
	fsync=x		If writing, fsync after every x blocks have been written
	startdelay=x	Start this thread x seconds after startup
	timeout=x	Terminate x seconds after startup
	offset=x	Start io at offset x (x string can include k/m/g)
	invalidate=x	Invalidate page cache for file prior to doing io
	sync=x		Use sync writes if x and writing
	mem=x		If x == malloc, use malloc for buffers. If x == shm,
			use shm for buffers. If x == mmap, use anon mmap.
	exitall		When one thread quits, terminate the others
	bwavgtime=x	Average bandwidth stats over an x msec window.
	create_serialize=x	If 'x', serialize file creation.
	create_fsync=x	If 'x', run fsync() after file creation.
	loops=x		Run the job 'x' number of times.
	verify=x	If 'x' == md5, use md5 for verifies. If 'x' == crc32,
			use crc32 for verifies. md5 is 'safer', but crc32 is
			a lot faster. Only makes sense for writing to a file.
	stonewall	Wait for preceeding jobs to end before running.
	numjobs=x	Create 'x' similar entries for this job
	thread		Use pthreads instead of forked jobs
	zonesize=x
	zoneskip=y	Zone options must be paired. If given, the job
			will skip y bytes for every x read/written. This
			can be used to gauge hard drive speed over the entire
			platter, without reading everything. Both x/y can
			include k/m/g suffix.
	iolog=x		Open and read io pattern from file 'x'. The file must
			contain one io action per line in the following format:
			rw, offset, length
			where with rw=0/1 for read/write, and the offset
			and length entries being in bytes.


Examples using a job file
-------------------------

A sample job file doing the same as above would look like this:

[read_file]
rw=0
bs=4096

[write_file]
rw=1
bs=16384

And fio would be invoked as:

$ fio -o1 -s -f file_with_above

The second example would look like this:

[rf1]
rw=0
prio=6

[rf2]
rw=0
prio=3

[rf3]
rw=0
prio=0
direct=1

And fio would be invoked as:

$ fio -o0 -s -b4096 -f file_with_above

'global' is a reserved keyword. When used as the filename, it sets the
default options for the threads following that section. It is possible
to have more than one global section in the file, as it only affects
subsequent jobs.

Also see the examples/ dir for sample job files.


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 now running: 2 : [ww] [5.73% done]

The characters inside the square brackets denote the current status of
each thread. The possible values (in typical life cycle order) are:

Idle	Run
----    ---
P		Thread setup, but not started.
C		Thread created and running, but not doing anything yet
	R	Running, doing sequential reads.
	r	Running, doing random reads.
	W	Running, doing sequential writes.
	w	Running, doing random writes.
V		Running, doing verification of written data.
E		Thread exited, not reaped by main thread yet.
_		Thread reaped.

The other values are fairly self explanatory - number of thread currently
running and doing io, and the estimated completion percentage.

When fio is done (or interrupted by ctrl-c), it will show the data for
each thread, group of threads, and disks in that order. For each data
direction, the output looks like:

Client1 (g=0): err= 0:
  write: io=    32MiB, bw=   666KiB/s, runt= 50320msec
    slat (msec): min=    0, max=  136, avg= 0.03, dev= 1.92
    clat (msec): min=    0, max=  631, avg=48.50, dev=86.82
    bw (KiB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, dev=681.68
  cpu        : usr=1.49%, sys=0.25%, ctx=7969

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,
they denote:

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
		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.
	clat=	Completion latency. Same names as slat, this denotes the
		time from submission to completion of the io pieces. For
		sync io, clat will usually be equal (or very close) to 0,
		as the time from submit to complete is basically just
		CPU time (io has already been done, see slat explanation).
	bw=	Bandwidth. Same names as the xlat stats, but also includes
		an approximate percentage of total aggregate bandwidth
		this thread received in this group. This last value is
		only really useful if the threads in this group are on the
		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.

After each client has been listed, the group statistics are printed. They
will look like this:

Run status group 0 (all jobs):
   READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
  WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec

For each data direction, it prints:

io=		Number of megabytes io performed.
aggrb=		Aggregate bandwidth of threads in this group.
minb=		The minimum average bandwidth a thread saw.
maxb=		The maximum average bandwidth a thread saw.
mint=		The minimum runtime of a thread.
maxt=		The maximum runtime of a thread.

And finally, the disk statistics are printed. They will look like this:

Disk stats (read/write):
  sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%

Each value is printed for both reads and writes, with reads first. The
numbers denote:

ios=		Number of ios performed by all groups.
merge=		Number of merges io the io scheduler.
ticks=		Number of ticks we kept the disk busy.
io_queue=	Total time spent in the disk queue.
util=		The disk utilization. A value of 100% means we kept the disk
		busy constantly, 50% would be a disk idling half of the time.