Table of contents ----------------- 1. Overview 2. How fio works 3. Running fio 4. Job file format 5. Detailed list of parameters 6. Normal output 7. Terse output 8. Trace file format 9. CPU idleness profiling 10. Verification and triggers 11. Log File Formats 1.0 Overview and history ------------------------ fio was originally written to save me the hassle of writing special test case programs when I wanted to test a specific workload, either for performance reasons or to find/reproduce a bug. The process of writing such a test app can be tiresome, especially if you have to do it often. Hence I needed a tool that would be able to simulate a given io workload without resorting to writing a tailored test case again and again. A test work load is difficult to define, though. There can be any number of processes or threads involved, and they can each be using their own way of generating io. You could have someone dirtying large amounts of memory in an memory mapped file, or maybe several threads issuing reads using asynchronous io. fio needed to be flexible enough to simulate both of these cases, and many more. 2.0 How fio works ----------------- The first step in getting fio to simulate a desired io workload, is writing a job file describing that specific setup. A job file may contain any number of threads and/or files - the typical contents of the job file is a global section defining shared parameters, and one or more job sections describing the jobs involved. When run, fio parses this file and sets everything up as described. If we break down a job from top to bottom, it contains the following basic parameters: IO type Defines the io pattern issued to the file(s). We may only be reading sequentially from this file(s), or we may be writing randomly. Or even mixing reads and writes, sequentially or randomly. Block size In how large chunks are we issuing io? This may be a single value, or it may describe a range of block sizes. IO size How much data are we going to be reading/writing. IO engine How do we issue io? We could be memory mapping the file, we could be using regular read/write, we could be using splice, async io, or even SG (SCSI generic sg). IO depth If the io engine is async, how large a queuing depth do we want to maintain? IO type Should we be doing buffered io, or direct/raw io? Num files How many files are we spreading the workload over. Num threads How many threads or processes should we spread this workload over. The above are the basic parameters defined for a workload, in addition there's a multitude of parameters that modify other aspects of how this job behaves. 3.0 Running fio --------------- See the README file for command line parameters, there are only a few of them. Running fio is normally the easiest part - you just give it the job file (or job files) as parameters: $ fio job_file and it will start doing what the job_file tells it to do. You can give more than one job file on the command line, fio will serialize the running of those files. Internally that is the same as using the 'stonewall' parameter described in the parameter section. If the job file contains only one job, you may as well just give the parameters on the command line. The command line parameters are identical to the job parameters, with a few extra that control global parameters (see README). For example, for the job file parameter iodepth=2, the mirror command line option would be --iodepth 2 or --iodepth=2. You can also use the command line for giving more than one job entry. For each --name option that fio sees, it will start a new job with that name. Command line entries following a --name entry will apply to that job, until there are no more entries or a new --name entry is seen. This is similar to the job file options, where each option applies to the current job until a new [] job entry is seen. fio does not need to run as root, except if the files or devices specified in the job section requires that. Some other options may also be restricted, such as memory locking, io scheduler switching, and decreasing the nice value. 4.0 Job file format ------------------- As previously described, fio accepts one or more job files describing what it is supposed to do. The job file format is the classic ini file, where the names enclosed in [] brackets define the job name. You are free to use any ascii name you want, except 'global' which has special meaning. A global section sets defaults for the jobs described in that file. A job may override a global section parameter, and a job file may even have several global sections if so desired. A job is only affected by a global section residing above it. If the first character in a line is a ';' or a '#', the entire line is discarded as a comment. So let's look at a really simple job file that defines two processes, each randomly reading from a 128MB file. ; -- start job file -- [global] rw=randread size=128m [job1] [job2] ; -- end job file -- As you can see, the job file sections themselves are empty as all the described parameters are shared. As no filename= option is given, fio makes up a filename for each of the jobs as it sees fit. On the command line, this job would look as follows: $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2 Let's look at an example that has a number of processes writing randomly to files. ; -- start job file -- [random-writers] ioengine=libaio iodepth=4 rw=randwrite bs=32k direct=0 size=64m numjobs=4 ; -- end job file -- Here we have no global section, as we only have one job defined anyway. We want to use async io here, with a depth of 4 for each file. We also increased the buffer size used to 32KB and define numjobs to 4 to fork 4 identical jobs. The result is 4 processes each randomly writing to their own 64MB file. Instead of using the above job file, you could have given the parameters on the command line. For this case, you would specify: $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4 When fio is utilized as a basis of any reasonably large test suite, it might be desirable to share a set of standardized settings across multiple job files. Instead of copy/pasting such settings, any section may pull in an external .fio file with 'include filename' directive, as in the following example: ; -- start job file including.fio -- [global] filename=/tmp/test filesize=1m include glob-include.fio [test] rw=randread bs=4k time_based=1 runtime=10 include test-include.fio ; -- end job file including.fio -- ; -- start job file glob-include.fio -- thread=1 group_reporting=1 ; -- end job file glob-include.fio -- ; -- start job file test-include.fio -- ioengine=libaio iodepth=4 ; -- end job file test-include.fio -- Settings pulled into a section apply to that section only (except global section). Include directives may be nested in that any included file may contain further include directive(s). Include files may not contain [] sections. 4.1 Environment variables ------------------------- fio also supports environment variable expansion in job files. Any sub-string of the form "${VARNAME}" as part of an option value (in other words, on the right of the `='), will be expanded to the value of the environment variable called VARNAME. If no such environment variable is defined, or VARNAME is the empty string, the empty string will be substituted. As an example, let's look at a sample fio invocation and job file: $ SIZE=64m NUMJOBS=4 fio jobfile.fio ; -- start job file -- [random-writers] rw=randwrite size=${SIZE} numjobs=${NUMJOBS} ; -- end job file -- This will expand to the following equivalent job file at runtime: ; -- start job file -- [random-writers] rw=randwrite size=64m numjobs=4 ; -- end job file -- fio ships with a few example job files, you can also look there for inspiration. 4.2 Reserved keywords --------------------- Additionally, fio has a set of reserved keywords that will be replaced internally with the appropriate value. Those keywords are: $pagesize The architecture page size of the running system $mb_memory Megabytes of total memory in the system $ncpus Number of online available CPUs These can be used on the command line or in the job file, and will be automatically substituted with the current system values when the job is run. Simple math is also supported on these keywords, so you can perform actions like: size=8*$mb_memory and get that properly expanded to 8 times the size of memory in the machine. 5.0 Detailed list of parameters ------------------------------- This section describes in details each parameter associated with a job. Some parameters take an option of a given type, such as an integer or a string. Anywhere a numeric value is required, an arithmetic expression may be used, provided it is surrounded by parentheses. Supported operators are: addition (+) subtraction (-) multiplication (*) division (/) modulus (%) exponentiation (^) For time values in expressions, units are microseconds by default. This is different than for time values not in expressions (not enclosed in parentheses). The following types are used: str String. This is a sequence of alpha characters. time Integer with possible time suffix. In seconds unless otherwise specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds, minutes, and hours, and accepts 'ms' (or 'msec') for milliseconds, and 'us' (or 'usec') for microseconds. int SI integer. A whole number value, which may contain a suffix describing the base of the number. Accepted suffixes are k/m/g/t/p, meaning kilo, mega, giga, tera, and peta. The suffix is not case sensitive, and you may also include trailing 'b' (eg 'kb' is the same as 'k'). So if you want to specify 4096, you could either write out '4096' or just give 4k. The suffixes signify base 2 values, so 1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the case, then 1000 is used as the multiplier. This can be handy for disks, since manufacturers generally use base 10 values when listing the capacity of a drive. If the option accepts an upper and lower range, use a colon ':' or minus '-' to separate such values. May also include a prefix to indicate numbers base. If 0x is used, the number is assumed to be hexadecimal. See irange. bool Boolean. Usually parsed as an integer, however only defined for true and false (1 and 0). irange Integer range with suffix. Allows value range to be given, such as 1024-4096. A colon may also be used as the separator, eg 1k:4k. If the option allows two sets of ranges, they can be specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see int. float_list A list of floating numbers, separated by a ':' character. With the above in mind, here follows the complete list of fio job parameters. name=str ASCII name of the job. This may be used to override the name printed by fio for this job. Otherwise the job name is used. On the command line this parameter has the special purpose of also signaling the start of a new job. wait_for=str Specifies the name of the already defined job to wait for. Single waitee name only may be specified. If set, the job won't be started until all workers of the waitee job are done. Wait_for operates on the job name basis, so there are a few limitations. First, the waitee must be defined prior to the waiter job (meaning no forward references). Second, if a job is being referenced as a waitee, it must have a unique name (no duplicate waitees). description=str Text description of the job. Doesn't do anything except dump this text description when this job is run. It's not parsed. directory=str Prefix filenames with this directory. Used to place files in a different location than "./". See the 'filename' option for escaping certain characters. filename=str Fio normally makes up a filename based on the job name, thread number, and file number. If you want to share files between threads in a job or several jobs, specify a filename for each of them to override the default. If the ioengine is file based, you can specify a number of files by separating the names with a ':' colon. So if you wanted a job to open /dev/sda and /dev/sdb as the two working files, you would use filename=/dev/sda:/dev/sdb. On Windows, disk devices are accessed as \\.\PhysicalDrive0 for the first device, \\.\PhysicalDrive1 for the second etc. Note: Windows and FreeBSD prevent write access to areas of the disk containing in-use data (e.g. filesystems). If the wanted filename does need to include a colon, then escape that with a '\' character. For instance, if the filename is "/dev/dsk/foo@3,0:c", then you would use filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning stdin or stdout. Which of the two depends on the read/write direction set. filename_format=str If sharing multiple files between jobs, it is usually necessary to have fio generate the exact names that you want. By default, fio will name a file based on the default file format specification of jobname.jobnumber.filenumber. With this option, that can be customized. Fio will recognize and replace the following keywords in this string: $jobname The name of the worker thread or process. $jobnum The incremental number of the worker thread or process. $filenum The incremental number of the file for that worker thread or process. To have dependent jobs share a set of files, this option can be set to have fio generate filenames that are shared between the two. For instance, if testfiles.$filenum is specified, file number 4 for any job will be named testfiles.4. The default of $jobname.$jobnum.$filenum will be used if no other format specifier is given. unique_filename=bool To avoid collisions between networked clients, fio defaults to prefixing any generated filenames (with a directory specified) with the source of the client connecting. To disable this behavior, set this option to 0. opendir=str Tell fio to recursively add any file it can find in this directory and down the file system tree. lockfile=str Fio defaults to not locking any files before it does IO to them. If a file or file descriptor is shared, fio can serialize IO to that file to make the end result consistent. This is usual for emulating real workloads that share files. The lock modes are: none No locking. The default. exclusive Only one thread/process may do IO, excluding all others. readwrite Read-write locking on the file. Many readers may access the file at the same time, but writes get exclusive access. readwrite=str rw=str Type of io pattern. Accepted values are: read Sequential reads write Sequential writes randwrite Random writes randread Random reads rw,readwrite Sequential mixed reads and writes randrw Random mixed reads and writes trimwrite Mixed trims and writes. Blocks will be trimmed first, then written to. Fio defaults to read if the option is not specified. For the mixed io types, the default is to split them 50/50. For certain types of io the result may still be skewed a bit, since the speed may be different. It is possible to specify a number of IO's to do before getting a new offset, this is done by appending a ':' to the end of the string given. For a random read, it would look like 'rw=randread:8' for passing in an offset modifier with a value of 8. If the suffix is used with a sequential IO pattern, then the value specified will be added to the generated offset for each IO. For instance, using rw=write:4k will skip 4k for every write. It turns sequential IO into sequential IO with holes. See the 'rw_sequencer' option. rw_sequencer=str If an offset modifier is given by appending a number to the rw= line, then this option controls how that number modifies the IO offset being generated. Accepted values are: sequential Generate sequential offset identical Generate the same offset 'sequential' is only useful for random IO, where fio would normally generate a new random offset for every IO. If you append eg 8 to randread, you would get a new random offset for every 8 IO's. The result would be a seek for only every 8 IO's, instead of for every IO. Use rw=randread:8 to specify that. As sequential IO is already sequential, setting 'sequential' for that would not result in any differences. 'identical' behaves in a similar fashion, except it sends the same offset 8 number of times before generating a new offset. kb_base=int The base unit for a kilobyte. The defacto base is 2^10, 1024. Storage manufacturers like to use 10^3 or 1000 as a base ten unit instead, for obvious reasons. Allow values are 1024 or 1000, with 1024 being the default. unified_rw_reporting=bool Fio normally reports statistics on a per data direction basis, meaning that read, write, and trim are accounted and reported separately. If this option is set, the fio will sum the results and report them as "mixed" instead. randrepeat=bool For random IO workloads, seed the generator in a predictable way so that results are repeatable across repetitions. Defaults to true. randseed=int Seed the random number generators based on this seed value, to be able to control what sequence of output is being generated. If not set, the random sequence depends on the randrepeat setting. fallocate=str Whether pre-allocation is performed when laying down files. Accepted values are: none Do not pre-allocate space posix Pre-allocate via posix_fallocate() keep Pre-allocate via fallocate() with FALLOC_FL_KEEP_SIZE set 0 Backward-compatible alias for 'none' 1 Backward-compatible alias for 'posix' May not be available on all supported platforms. 'keep' is only available on Linux.If using ZFS on Solaris this must be set to 'none' because ZFS doesn't support it. Default: 'posix'. fadvise_hint=bool By default, fio will use fadvise() to advise the kernel on what IO patterns it is likely to issue. Sometimes you want to test specific IO patterns without telling the kernel about it, in which case you can disable this option. If set, fio will use POSIX_FADV_SEQUENTIAL for sequential IO and POSIX_FADV_RANDOM for random IO. fadvise_stream=int Notify the kernel what write stream ID to place these writes under. Only supported on Linux. Note, this option may change going forward. size=int The total size of file io for this job. Fio will run until this many bytes has been transferred, unless runtime is limited by other options (such as 'runtime', for instance, or increased/decreased by 'io_size'). Unless specific nrfiles and filesize options are given, fio will divide this size between the available files specified by the job. If not set, fio will use the full size of the given files or devices. If the files do not exist, size must be given. It is also possible to give size as a percentage between 1 and 100. If size=20% is given, fio will use 20% of the full size of the given files or devices. io_size=int io_limit=int Normally fio operates within the region set by 'size', which means that the 'size' option sets both the region and size of IO to be performed. Sometimes that is not what you want. With this option, it is possible to define just the amount of IO that fio should do. For instance, if 'size' is set to 20G and 'io_size' is set to 5G, fio will perform IO within the first 20G but exit when 5G have been done. The opposite is also possible - if 'size' is set to 20G, and 'io_size' is set to 40G, then fio will do 40G of IO within the 0..20G region. filesize=int Individual file sizes. May be a range, in which case fio will select sizes for files at random within the given range and limited to 'size' in total (if that is given). If not given, each created file is the same size. file_append=bool Perform IO after the end of the file. Normally fio will operate within the size of a file. If this option is set, then fio will append to the file instead. This has identical behavior to setting offset to the size of a file. This option is ignored on non-regular files. fill_device=bool fill_fs=bool Sets size to something really large and waits for ENOSPC (no space left on device) as the terminating condition. Only makes sense with sequential write. For a read workload, the mount point will be filled first then IO started on the result. This option doesn't make sense if operating on a raw device node, since the size of that is already known by the file system. Additionally, writing beyond end-of-device will not return ENOSPC there. blocksize=int bs=int The block size used for the io units. Defaults to 4k. Values can be given for both read and writes. If a single int is given, it will apply to both. If a second int is specified after a comma, it will apply to writes only. In other words, the format is either bs=read_and_write or bs=read,write,trim. bs=4k,8k will thus use 4k blocks for reads, 8k blocks for writes, and 8k for trims. You can terminate the list with a trailing comma. bs=4k,8k, would use the default value for trims.. If you only wish to set the write size, you can do so by passing an empty read size - bs=,8k will set 8k for writes and leave the read default value. blockalign=int ba=int At what boundary to align random IO offsets. Defaults to the same as 'blocksize' the minimum blocksize given. Minimum alignment is typically 512b for using direct IO, though it usually depends on the hardware block size. This option is mutually exclusive with using a random map for files, so it will turn off that option. blocksize_range=irange bsrange=irange Instead of giving a single block size, specify a range and fio will mix the issued io block sizes. The issued io unit will always be a multiple of the minimum value given (also see bs_unaligned). Applies to both reads and writes, however a second range can be given after a comma. See bs=. bssplit=str Sometimes you want even finer grained control of the block sizes issued, not just an even split between them. This option allows you to weight various block sizes, so that you are able to define a specific amount of block sizes issued. The format for this option is: bssplit=blocksize/percentage:blocksize/percentage for as many block sizes as needed. So if you want to define a workload that has 50% 64k blocks, 10% 4k blocks, and 40% 32k blocks, you would write: bssplit=4k/10:64k/50:32k/40 Ordering does not matter. If the percentage is left blank, fio will fill in the remaining values evenly. So a bssplit option like this one: bssplit=4k/50:1k/:32k/ would have 50% 4k ios, and 25% 1k and 32k ios. The percentages always add up to 100, if bssplit is given a range that adds up to more, it will error out. bssplit also supports giving separate splits to reads and writes. The format is identical to what bs= accepts. You have to separate the read and write parts with a comma. So if you want a workload that has 50% 2k reads and 50% 4k reads, while having 90% 4k writes and 10% 8k writes, you would specify: bssplit=2k/50:4k/50,4k/90:8k/10 blocksize_unaligned bs_unaligned If this option is given, any byte size value within bsrange may be used as a block range. This typically wont work with direct IO, as that normally requires sector alignment. bs_is_seq_rand If this option is set, fio will use the normal read,write blocksize settings as sequential,random instead. Any random read or write will use the WRITE blocksize settings, and any sequential read or write will use the READ blocksize setting. zero_buffers If this option is given, fio will init the IO buffers to all zeroes. The default is to fill them with random data. refill_buffers If this option is given, fio will refill the IO buffers on every submit. The default is to only fill it at init time and reuse that data. Only makes sense if zero_buffers isn't specified, naturally. If data verification is enabled, refill_buffers is also automatically enabled. scramble_buffers=bool If refill_buffers is too costly and the target is using data deduplication, then setting this option will slightly modify the IO buffer contents to defeat normal de-dupe attempts. This is not enough to defeat more clever block compression attempts, but it will stop naive dedupe of blocks. Default: true. buffer_compress_percentage=int If this is set, then fio will attempt to provide IO buffer content (on WRITEs) that compress to the specified level. Fio does this by providing a mix of random data and a fixed pattern. The fixed pattern is either zeroes, or the pattern specified by buffer_pattern. If the pattern option is used, it might skew the compression ratio slightly. Note that this is per block size unit, for file/disk wide compression level that matches this setting, you'll also want to set refill_buffers. buffer_compress_chunk=int See buffer_compress_percentage. This setting allows fio to manage how big the ranges of random data and zeroed data is. Without this set, fio will provide buffer_compress_percentage of blocksize random data, followed by the remaining zeroed. With this set to some chunk size smaller than the block size, fio can alternate random and zeroed data throughout the IO buffer. buffer_pattern=str If set, fio will fill the io buffers with this pattern. If not set, the contents of io buffers is defined by the other options related to buffer contents. The setting can be any pattern of bytes, and can be prefixed with 0x for hex values. It may also be a string, where the string must then be wrapped with "", e.g.: buffer_pattern="abcd" or buffer_pattern=-12 or buffer_pattern=0xdeadface Also you can combine everything together in any order: buffer_pattern=0xdeadface"abcd"-12 dedupe_percentage=int If set, fio will generate this percentage of identical buffers when writing. These buffers will be naturally dedupable. The contents of the buffers depend on what other buffer compression settings have been set. It's possible to have the individual buffers either fully compressible, or not at all. This option only controls the distribution of unique buffers. nrfiles=int Number of files to use for this job. Defaults to 1. openfiles=int Number of files to keep open at the same time. Defaults to the same as nrfiles, can be set smaller to limit the number simultaneous opens. file_service_type=str Defines how fio decides which file from a job to service next. The following types are defined: random Just choose a file at random. roundrobin Round robin over open files. This is the default. sequential Finish one file before moving on to the next. Multiple files can still be open depending on 'openfiles'. zipf Use a zipfian distribution to decide what file to access. pareto Use a pareto distribution to decide what file to access. gauss Use a gaussian (normal) distribution to decide what file to access. For random, roundrobin, and sequential, a postfix can be appended to tell fio how many I/Os to issue before switching to a new file. For example, specifying 'file_service_type=random:8' would cause fio to issue 8 I/Os before selecting a new file at random. For the non-uniform distributions, a floating point postfix can be given to influence how the distribution is skewed. See 'random_distribution' for a description of how that would work. ioengine=str Defines how the job issues io to the file. The following types are defined: sync Basic read(2) or write(2) io. lseek(2) is used to position the io location. psync Basic pread(2) or pwrite(2) io. Default on all supported operating systems except for Windows. vsync Basic readv(2) or writev(2) IO. pvsync Basic preadv(2) or pwritev(2) IO. pvsync2 Basic preadv2(2) or pwritev2(2) IO. libaio Linux native asynchronous io. Note that Linux may only support queued behaviour with non-buffered IO (set direct=1 or buffered=0). This engine defines engine specific options. posixaio glibc posix asynchronous io. solarisaio Solaris native asynchronous io. windowsaio Windows native asynchronous io. Default on Windows. mmap File is memory mapped and data copied to/from using memcpy(3). splice splice(2) is used to transfer the data and vmsplice(2) to transfer data from user space to the kernel. sg SCSI generic sg v3 io. May either be synchronous using the SG_IO ioctl, or if the target is an sg character device we use read(2) and write(2) for asynchronous io. null Doesn't transfer any data, just pretends to. This is mainly used to exercise fio itself and for debugging/testing purposes. net Transfer over the network to given host:port. Depending on the protocol used, the hostname, port, listen and filename options are used to specify what sort of connection to make, while the protocol option determines which protocol will be used. This engine defines engine specific options. netsplice Like net, but uses splice/vmsplice to map data and send/receive. This engine defines engine specific options. cpuio Doesn't transfer any data, but burns CPU cycles according to the cpuload= and cpuchunks= options. Setting cpuload=85 will cause that job to do nothing but burn 85% of the CPU. In case of SMP machines, use numjobs= to get desired CPU usage, as the cpuload only loads a single CPU at the desired rate. A job never finishes unless there is at least one non-cpuio job. guasi The GUASI IO engine is the Generic Userspace Asyncronous Syscall Interface approach to async IO. See http://www.xmailserver.org/guasi-lib.html for more info on GUASI. rdma The RDMA I/O engine supports both RDMA memory semantics (RDMA_WRITE/RDMA_READ) and channel semantics (Send/Recv) for the InfiniBand, RoCE and iWARP protocols. falloc IO engine that does regular fallocate to simulate data transfer as fio ioengine. DDIR_READ does fallocate(,mode = keep_size,) DDIR_WRITE does fallocate(,mode = 0) DDIR_TRIM does fallocate(,mode = punch_hole) e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate defragment activity in request to DDIR_WRITE event rbd IO engine supporting direct access to Ceph Rados Block Devices (RBD) via librbd without the need to use the kernel rbd driver. This ioengine defines engine specific options. gfapi Using Glusterfs libgfapi sync interface to direct access to Glusterfs volumes without options. gfapi_async Using Glusterfs libgfapi async interface to direct access to Glusterfs volumes without having to go through FUSE. This ioengine defines engine specific options. libhdfs Read and write through Hadoop (HDFS). This engine interprets offsets a little differently. In HDFS, files once created cannot be modified. So random writes are not possible. To imitate this, libhdfs engine creates bunch of small files, and engine will pick a file out of those files based on the offset generated by fio backend. Each jobs uses it's own connection to HDFS. mtd Read, write and erase an MTD character device (e.g., /dev/mtd0). Discards are treated as erases. Depending on the underlying device type, the I/O may have to go in a certain pattern, e.g., on NAND, writing sequentially to erase blocks and discarding before overwriting. The writetrim mode works well for this constraint. pmemblk Read and write through the NVML libpmemblk interface. external Prefix to specify loading an external IO engine object file. Append the engine filename, eg ioengine=external:/tmp/foo.o to load ioengine foo.o in /tmp. iodepth=int This defines how many io units to keep in flight against the file. The default is 1 for each file defined in this job, can be overridden with a larger value for higher concurrency. Note that increasing iodepth beyond 1 will not affect synchronous ioengines (except for small degress when verify_async is in use). Even async engines may impose OS restrictions causing the desired depth not to be achieved. This may happen on Linux when using libaio and not setting direct=1, since buffered IO is not async on that OS. Keep an eye on the IO depth distribution in the fio output to verify that the achieved depth is as expected. Default: 1. iodepth_batch_submit=int iodepth_batch=int This defines how many pieces of IO to submit at once. It defaults to 1 which means that we submit each IO as soon as it is available, but can be raised to submit bigger batches of IO at the time. If it is set to 0 the iodepth value will be used. iodepth_batch_complete_min=int iodepth_batch_complete=int This defines how many pieces of IO to retrieve at once. It defaults to 1 which means that we'll ask for a minimum of 1 IO in the retrieval process from the kernel. The IO retrieval will go on until we hit the limit set by iodepth_low. If this variable is set to 0, then fio will always check for completed events before queuing more IO. This helps reduce IO latency, at the cost of more retrieval system calls. iodepth_batch_complete_max=int This defines maximum pieces of IO to retrieve at once. This variable should be used along with iodepth_batch_complete_min=int variable, specifying the range of min and max amount of IO which should be retrieved. By default it is equal to iodepth_batch_complete_min value. Example #1: iodepth_batch_complete_min=1 iodepth_batch_complete_max= which means that we will retrieve at least 1 IO and up to the whole submitted queue depth. If none of IO has been completed yet, we will wait. Example #2: iodepth_batch_complete_min=0 iodepth_batch_complete_max= which means that we can retrieve up to the whole submitted queue depth, but if none of IO has been completed yet, we will NOT wait and immediately exit the system call. In this example we simply do polling. iodepth_low=int The low water mark indicating when to start filling the queue again. Defaults to the same as iodepth, meaning that fio will attempt to keep the queue full at all times. If iodepth is set to eg 16 and iodepth_low is set to 4, then after fio has filled the queue of 16 requests, it will let the depth drain down to 4 before starting to fill it again. io_submit_mode=str This option controls how fio submits the IO to the IO engine. The default is 'inline', which means that the fio job threads submit and reap IO directly. If set to 'offload', the job threads will offload IO submission to a dedicated pool of IO threads. This requires some coordination and thus has a bit of extra overhead, especially for lower queue depth IO where it can increase latencies. The benefit is that fio can manage submission rates independently of the device completion rates. This avoids skewed latency reporting if IO gets back up on the device side (the coordinated omission problem). direct=bool If value is true, use non-buffered io. This is usually O_DIRECT. Note that ZFS on Solaris doesn't support direct io. On Windows the synchronous ioengines don't support direct io. atomic=bool If value is true, attempt to use atomic direct IO. Atomic writes are guaranteed to be stable once acknowledged by the operating system. Only Linux supports O_ATOMIC right now. buffered=bool If value is true, use buffered io. This is the opposite of the 'direct' option. Defaults to true. offset=int Start io at the given offset in the file. The data before the given offset will not be touched. This effectively caps the file size at real_size - offset. offset_increment=int If this is provided, then the real offset becomes offset + offset_increment * thread_number, where the thread number is a counter that starts at 0 and is incremented for each sub-job (i.e. when numjobs option is specified). This option is useful if there are several jobs which are intended to operate on a file in parallel disjoint segments, with even spacing between the starting points. number_ios=int Fio will normally perform IOs until it has exhausted the size of the region set by size=, or if it exhaust the allocated time (or hits an error condition). With this setting, the range/size can be set independently of the number of IOs to perform. When fio reaches this number, it will exit normally and report status. Note that this does not extend the amount of IO that will be done, it will only stop fio if this condition is met before other end-of-job criteria. fsync=int If writing to a file, issue a sync of the dirty data for every number of blocks given. For example, if you give 32 as a parameter, fio will sync the file for every 32 writes issued. If fio is using non-buffered io, we may not sync the file. The exception is the sg io engine, which synchronizes the disk cache anyway. fdatasync=int Like fsync= but uses fdatasync() to only sync data and not metadata blocks. In FreeBSD and Windows there is no fdatasync(), this falls back to using fsync() sync_file_range=str:val Use sync_file_range() for every 'val' number of write operations. Fio will track range of writes that have happened since the last sync_file_range() call. 'str' can currently be one or more of: wait_before SYNC_FILE_RANGE_WAIT_BEFORE write SYNC_FILE_RANGE_WRITE wait_after SYNC_FILE_RANGE_WAIT_AFTER So if you do sync_file_range=wait_before,write:8, fio would use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for every 8 writes. Also see the sync_file_range(2) man page. This option is Linux specific. overwrite=bool If true, writes to a file will always overwrite existing data. If the file doesn't already exist, it will be created before the write phase begins. If the file exists and is large enough for the specified write phase, nothing will be done. end_fsync=bool If true, fsync file contents when a write stage has completed. fsync_on_close=bool If true, fio will fsync() a dirty file on close. This differs from end_fsync in that it will happen on every file close, not just at the end of the job. rwmixread=int How large a percentage of the mix should be reads. rwmixwrite=int How large a percentage of the mix should be writes. If both rwmixread and rwmixwrite is given and the values do not add up to 100%, the latter of the two will be used to override the first. This may interfere with a given rate setting, if fio is asked to limit reads or writes to a certain rate. If that is the case, then the distribution may be skewed. random_distribution=str:float By default, fio will use a completely uniform random distribution when asked to perform random IO. Sometimes it is useful to skew the distribution in specific ways, ensuring that some parts of the data is more hot than others. fio includes the following distribution models: random Uniform random distribution zipf Zipf distribution pareto Pareto distribution gauss Normal (gaussian) distribution zoned Zoned random distribution When using a zipf or pareto distribution, an input value is also needed to define the access pattern. For zipf, this is the zipf theta. For pareto, it's the pareto power. Fio includes a test program, genzipf, that can be used visualize what the given input values will yield in terms of hit rates. If you wanted to use zipf with a theta of 1.2, you would use random_distribution=zipf:1.2 as the option. If a non-uniform model is used, fio will disable use of the random map. For the gauss distribution, a normal deviation is supplied as a value between 0 and 100. For a zoned distribution, fio supports specifying percentages of IO access that should fall within what range of the file or device. For example, given a criteria of: 60% of accesses should be to the first 10% 30% of accesses should be to the next 20% 8% of accesses should be to to the next 30% 2% of accesses should be to the next 40% we can define that through zoning of the random accesses. For the above example, the user would do: random_distribution=zoned:60/10:30/20:8/30:2/40 similarly to how bssplit works for setting ranges and percentages of block sizes. Like bssplit, it's possible to specify separate zones for reads, writes, and trims. If just one set is given, it'll apply to all of them. percentage_random=int For a random workload, set how big a percentage should be random. This defaults to 100%, in which case the workload is fully random. It can be set from anywhere from 0 to 100. Setting it to 0 would make the workload fully sequential. Any setting in between will result in a random mix of sequential and random IO, at the given percentages. It is possible to set different values for reads, writes, and trim. To do so, simply use a comma separated list. See blocksize. norandommap Normally fio will cover every block of the file when doing random IO. If this option is given, fio will just get a new random offset without looking at past io history. This means that some blocks may not be read or written, and that some blocks may be read/written more than once. If this option is used with verify= and multiple blocksizes (via bsrange=), only intact blocks are verified, i.e., partially-overwritten blocks are ignored. softrandommap=bool See norandommap. If fio runs with the random block map enabled and it fails to allocate the map, if this option is set it will continue without a random block map. As coverage will not be as complete as with random maps, this option is disabled by default. random_generator=str Fio supports the following engines for generating IO offsets for random IO: tausworthe Strong 2^88 cycle random number generator lfsr Linear feedback shift register generator tausworthe64 Strong 64-bit 2^258 cycle random number generator Tausworthe is a strong random number generator, but it requires tracking on the side if we want to ensure that blocks are only read or written once. LFSR guarantees that we never generate the same offset twice, and it's also less computationally expensive. It's not a true random generator, however, though for IO purposes it's typically good enough. LFSR only works with single block sizes, not with workloads that use multiple block sizes. If used with such a workload, fio may read or write some blocks multiple times. The default value is tausworthe, unless the required space exceeds 2^32 blocks. If it does, then tausworthe64 is selected automatically. nice=int Run the job with the given nice value. See man nice(2). On Windows, values less than -15 set the process class to "High"; -1 through -15 set "Above Normal"; 1 through 15 "Below Normal"; and above 15 "Idle" priority class. prio=int Set the io priority value of this job. Linux limits us to a positive value between 0 and 7, with 0 being the highest. See man ionice(1). Refer to an appropriate manpage for other operating systems since meaning of priority may differ. prioclass=int Set the io priority class. See man ionice(1). thinktime=int Stall the job x microseconds after an io has completed before issuing the next. May be used to simulate processing being done by an application. See thinktime_blocks and thinktime_spin. thinktime_spin=int Only valid if thinktime is set - pretend to spend CPU time doing something with the data received, before falling back to sleeping for the rest of the period specified by thinktime. thinktime_blocks=int Only valid if thinktime is set - control how many blocks to issue, before waiting 'thinktime' usecs. If not set, defaults to 1 which will make fio wait 'thinktime' usecs after every block. This effectively makes any queue depth setting redundant, since no more than 1 IO will be queued before we have to complete it and do our thinktime. In other words, this setting effectively caps the queue depth if the latter is larger. rate=int Cap the bandwidth used by this job. The number is in bytes/sec, the normal suffix rules apply. You can use rate=500k to limit reads and writes to 500k each, or you can specify read and writes separately. Using rate=1m,500k would limit reads to 1MB/sec and writes to 500KB/sec. Capping only reads or writes can be done with rate=,500k or rate=500k,. The former will only limit writes (to 500KB/sec), the latter will only limit reads. rate_min=int Tell fio to do whatever it can to maintain at least this bandwidth. Failing to meet this requirement, will cause the job to exit. The same format as rate is used for read vs write separation. rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same as rate, just specified independently of bandwidth. If the job is given a block size range instead of a fixed value, the smallest block size is used as the metric. The same format as rate is used for read vs write separation. rate_iops_min=int If fio doesn't meet this rate of IO, it will cause the job to exit. The same format as rate is used for read vs write separation. rate_process=str This option controls how fio manages rated IO submissions. The default is 'linear', which submits IO in a linear fashion with fixed delays between IOs that gets adjusted based on IO completion rates. If this is set to 'poisson', fio will submit IO based on a more real world random request flow, known as the Poisson process (https://en.wikipedia.org/wiki/Poisson_process). The lambda will be 10^6 / IOPS for the given workload. latency_target=int If set, fio will attempt to find the max performance point that the given workload will run at while maintaining a latency below this target. The values is given in microseconds. See latency_window and latency_percentile latency_window=int Used with latency_target to specify the sample window that the job is run at varying queue depths to test the performance. The value is given in microseconds. latency_percentile=float The percentage of IOs that must fall within the criteria specified by latency_target and latency_window. If not set, this defaults to 100.0, meaning that all IOs must be equal or below to the value set by latency_target. max_latency=int If set, fio will exit the job if it exceeds this maximum latency. It will exit with an ETIME error. rate_cycle=int Average bandwidth for 'rate' and 'rate_min' over this number of milliseconds. cpumask=int Set the CPU affinity of this job. The parameter given is a bitmask of allowed CPU's the job may run on. So if you want the allowed CPUs to be 1 and 5, you would pass the decimal value of (1 << 1 | 1 << 5), or 34. See man sched_setaffinity(2). This may not work on all supported operating systems or kernel versions. This option doesn't work well for a higher CPU count than what you can store in an integer mask, so it can only control cpus 1-32. For boxes with larger CPU counts, use cpus_allowed. cpus_allowed=str Controls the same options as cpumask, but it allows a text setting of the permitted CPUs instead. So to use CPUs 1 and 5, you would specify cpus_allowed=1,5. This options also allows a range of CPUs. Say you wanted a binding to CPUs 1, 5, and 8-15, you would set cpus_allowed=1,5,8-15. cpus_allowed_policy=str Set the policy of how fio distributes the CPUs specified by cpus_allowed or cpumask. Two policies are supported: shared All jobs will share the CPU set specified. split Each job will get a unique CPU from the CPU set. 'shared' is the default behaviour, if the option isn't specified. If split is specified, then fio will will assign one cpu per job. If not enough CPUs are given for the jobs listed, then fio will roundrobin the CPUs in the set. numa_cpu_nodes=str Set this job running on specified NUMA nodes' CPUs. The arguments allow comma delimited list of cpu numbers, A-B ranges, or 'all'. Note, to enable numa options support, fio must be built on a system with libnuma-dev(el) installed. numa_mem_policy=str Set this job's memory policy and corresponding NUMA nodes. Format of the arguments: [:] `mode' is one of the following memory policy: default, prefer, bind, interleave, local For `default' and `local' memory policy, no node is needed to be specified. For `prefer', only one node is allowed. For `bind' and `interleave', it allow comma delimited list of numbers, A-B ranges, or 'all'. startdelay=time Start this job the specified number of seconds after fio has started. Only useful if the job file contains several jobs, and you want to delay starting some jobs to a certain time. runtime=time Tell fio to terminate processing after the specified number of seconds. It can be quite hard to determine for how long a specified job will run, so this parameter is handy to cap the total runtime to a given time. time_based If set, fio will run for the duration of the runtime specified even if the file(s) are completely read or written. It will simply loop over the same workload as many times as the runtime allows. ramp_time=time If set, fio will run the specified workload for this amount of time before logging any performance numbers. Useful for letting performance settle before logging results, thus minimizing the runtime required for stable results. Note that the ramp_time is considered lead in time for a job, thus it will increase the total runtime if a special timeout or runtime is specified. invalidate=bool Invalidate the buffer/page cache parts for this file prior to starting io. Defaults to true. sync=bool Use sync io for buffered writes. For the majority of the io engines, this means using O_SYNC. iomem=str mem=str Fio can use various types of memory as the io unit buffer. The allowed values are: malloc Use memory from malloc(3) as the buffers. Default memory type. shm Use shared memory as the buffers. Allocated through shmget(2). shmhuge Same as shm, but use huge pages as backing. mmap Use mmap to allocate buffers. May either be anonymous memory, or can be file backed if a filename is given after the option. The format is mem=mmap:/path/to/file. mmaphuge Use a memory mapped huge file as the buffer backing. Append filename after mmaphuge, ala mem=mmaphuge:/hugetlbfs/file mmapshared Same as mmap, but use a MMAP_SHARED mapping. The area allocated is a function of the maximum allowed bs size for the job, multiplied by the io depth given. Note that for shmhuge and mmaphuge to work, the system must have free huge pages allocated. This can normally be checked and set by reading/writing /proc/sys/vm/nr_hugepages on a Linux system. Fio assumes a huge page is 4MB in size. So to calculate the number of huge pages you need for a given job file, add up the io depth of all jobs (normally one unless iodepth= is used) and multiply by the maximum bs set. Then divide that number by the huge page size. You can see the size of the huge pages in /proc/meminfo. If no huge pages are allocated by having a non-zero number in nr_hugepages, using mmaphuge or shmhuge will fail. Also see hugepage-size. mmaphuge also needs to have hugetlbfs mounted and the file location should point there. So if it's mounted in /huge, you would use mem=mmaphuge:/huge/somefile. iomem_align=int This indicates the memory alignment of the IO memory buffers. Note that the given alignment is applied to the first IO unit buffer, if using iodepth the alignment of the following buffers are given by the bs used. In other words, if using a bs that is a multiple of the page sized in the system, all buffers will be aligned to this value. If using a bs that is not page aligned, the alignment of subsequent IO memory buffers is the sum of the iomem_align and bs used. hugepage-size=int Defines the size of a huge page. Must at least be equal to the system setting, see /proc/meminfo. Defaults to 4MB. Should probably always be a multiple of megabytes, so using hugepage-size=Xm is the preferred way to set this to avoid setting a non-pow-2 bad value. exitall When one job finishes, terminate the rest. The default is to wait for each job to finish, sometimes that is not the desired action. exitall_on_error When one job finishes in error, terminate the rest. The default is to wait for each job to finish. bwavgtime=int Average the calculated bandwidth over the given time. Value is specified in milliseconds. If the job also does bandwidth logging through 'write_bw_log', then the minimum of this option and 'log_avg_msec' will be used. Default: 500ms. iopsavgtime=int Average the calculated IOPS over the given time. Value is specified in milliseconds. If the job also does IOPS logging through 'write_iops_log', then the minimum of this option and 'log_avg_msec' will be used. Default: 500ms. create_serialize=bool If true, serialize the file creation for the jobs. This may be handy to avoid interleaving of data files, which may greatly depend on the filesystem used and even the number of processors in the system. create_fsync=bool fsync the data file after creation. This is the default. create_on_open=bool Don't pre-setup the files for IO, just create open() when it's time to do IO to that file. create_only=bool If true, fio will only run the setup phase of the job. If files need to be laid out or updated on disk, only that will be done. The actual job contents are not executed. allow_file_create=bool If true, fio is permitted to create files as part of its workload. This is the default behavior. If this option is false, then fio will error out if the files it needs to use don't already exist. Default: true. allow_mounted_write=bool If this isn't set, fio will abort jobs that are destructive (eg that write) to what appears to be a mounted device or partition. This should help catch creating inadvertently destructive tests, not realizing that the test will destroy data on the mounted file system. Default: false. pre_read=bool If this is given, files will be pre-read into memory before starting the given IO operation. This will also clear the 'invalidate' flag, since it is pointless to pre-read and then drop the cache. This will only work for IO engines that are seek-able, since they allow you to read the same data multiple times. Thus it will not work on eg network or splice IO. unlink=bool Unlink the job files when done. Not the default, as repeated runs of that job would then waste time recreating the file set again and again. unlink_each_loop=bool Unlink job files after each iteration or loop. loops=int Run the specified number of iterations of this job. Used to repeat the same workload a given number of times. Defaults to 1. verify_only Do not perform specified workload---only verify data still matches previous invocation of this workload. This option allows one to check data multiple times at a later date without overwriting it. This option makes sense only for workloads that write data, and does not support workloads with the time_based option set. do_verify=bool Run the verify phase after a write phase. Only makes sense if verify is set. Defaults to 1. verify=str If writing to a file, fio can verify the file contents after each iteration of the job. Each verification method also implies verification of special header, which is written to the beginning of each block. This header also includes meta information, like offset of the block, block number, timestamp when block was written, etc. verify=str can be combined with verify_pattern=str option. The allowed values are: md5 Use an md5 sum of the data area and store it in the header of each block. crc64 Use an experimental crc64 sum of the data area and store it in the header of each block. crc32c Use a crc32c sum of the data area and store it in the header of each block. crc32c-intel Use hardware assisted crc32c calculation provided on SSE4.2 enabled processors. Falls back to regular software crc32c, if not supported by the system. crc32 Use a crc32 sum of the data area and store it in the header of each block. crc16 Use a crc16 sum of the data area and store it in the header of each block. crc7 Use a crc7 sum of the data area and store it in the header of each block. xxhash Use xxhash as the checksum function. Generally the fastest software checksum that fio supports. sha512 Use sha512 as the checksum function. sha256 Use sha256 as the checksum function. sha1 Use optimized sha1 as the checksum function. meta This option is deprecated, since now meta information is included in generic verification header and meta verification happens by default. For detailed information see the description of the verify=str setting. This option is kept because of compatibility's sake with old configurations. Do not use it. pattern Verify a strict pattern. Normally fio includes a header with some basic information and checksumming, but if this option is set, only the specific pattern set with 'verify_pattern' is verified. null Only pretend to verify. Useful for testing internals with ioengine=null, not for much else. This option can be used for repeated burn-in tests of a system to make sure that the written data is also correctly read back. If the data direction given is a read or random read, fio will assume that it should verify a previously written file. If the data direction includes any form of write, the verify will be of the newly written data. verifysort=bool If set, fio will sort written verify blocks when it deems it faster to read them back in a sorted manner. This is often the case when overwriting an existing file, since the blocks are already laid out in the file system. You can ignore this option unless doing huge amounts of really fast IO where the red-black tree sorting CPU time becomes significant. verify_offset=int Swap the verification header with data somewhere else in the block before writing. Its swapped back before verifying. verify_interval=int Write the verification header at a finer granularity than the blocksize. It will be written for chunks the size of header_interval. blocksize should divide this evenly. verify_pattern=str If set, fio will fill the io buffers with this pattern. Fio defaults to filling with totally random bytes, but sometimes it's interesting to fill with a known pattern for io verification purposes. Depending on the width of the pattern, fio will fill 1/2/3/4 bytes of the buffer at the time(it can be either a decimal or a hex number). The verify_pattern if larger than a 32-bit quantity has to be a hex number that starts with either "0x" or "0X". Use with verify=str. Also, verify_pattern supports %o format, which means that for each block offset will be written and then verified back, e.g.: verify_pattern=%o Or use combination of everything: verify_pattern=0xff%o"abcd"-12 verify_fatal=bool Normally fio will keep checking the entire contents before quitting on a block verification failure. If this option is set, fio will exit the job on the first observed failure. verify_dump=bool If set, dump the contents of both the original data block and the data block we read off disk to files. This allows later analysis to inspect just what kind of data corruption occurred. Off by default. verify_async=int Fio will normally verify IO inline from the submitting thread. This option takes an integer describing how many async offload threads to create for IO verification instead, causing fio to offload the duty of verifying IO contents to one or more separate threads. If using this offload option, even sync IO engines can benefit from using an iodepth setting higher than 1, as it allows them to have IO in flight while verifies are running. verify_async_cpus=str Tell fio to set the given CPU affinity on the async IO verification threads. See cpus_allowed for the format used. verify_backlog=int Fio will normally verify the written contents of a job that utilizes verify once that job has completed. In other words, everything is written then everything is read back and verified. You may want to verify continually instead for a variety of reasons. Fio stores the meta data associated with an IO block in memory, so for large verify workloads, quite a bit of memory would be used up holding this meta data. If this option is enabled, fio will write only N blocks before verifying these blocks. verify_backlog_batch=int Control how many blocks fio will verify if verify_backlog is set. If not set, will default to the value of verify_backlog (meaning the entire queue is read back and verified). If verify_backlog_batch is less than verify_backlog then not all blocks will be verified, if verify_backlog_batch is larger than verify_backlog, some blocks will be verified more than once. verify_state_save=bool When a job exits during the write phase of a verify workload, save its current state. This allows fio to replay up until that point, if the verify state is loaded for the verify read phase. The format of the filename is, roughly, ---verify.state. is "local" for a local run, "sock" for a client/server socket connection, and "ip" (192.168.0.1, for instance) for a networked client/server connection. verify_state_load=bool If a verify termination trigger was used, fio stores the current write state of each thread. This can be used at verification time so that fio knows how far it should verify. Without this information, fio will run a full verification pass, according to the settings in the job file used. stonewall wait_for_previous Wait for preceding jobs in the job file to exit, before starting this one. Can be used to insert serialization points in the job file. A stone wall also implies starting a new reporting group. new_group Start a new reporting group. See: group_reporting. numjobs=int Create the specified number of clones of this job. May be used to setup a larger number of threads/processes doing the same thing. Each thread is reported separately; to see statistics for all clones as a whole, use group_reporting in conjunction with new_group. group_reporting It may sometimes be interesting to display statistics for groups of jobs as a whole instead of for each individual job. This is especially true if 'numjobs' is used; looking at individual thread/process output quickly becomes unwieldy. To see the final report per-group instead of per-job, use 'group_reporting'. Jobs in a file will be part of the same reporting group, unless if separated by a stonewall, or by using 'new_group'. thread fio defaults to forking jobs, however if this option is given, fio will use pthread_create(3) to create threads instead. zonesize=int Divide a file into zones of the specified size. See zoneskip. zoneskip=int Skip the specified number of bytes when zonesize data has been read. The two zone options can be used to only do io on zones of a file. write_iolog=str Write the issued io patterns to the specified file. See read_iolog. Specify a separate file for each job, otherwise the iologs will be interspersed and the file may be corrupt. read_iolog=str Open an iolog with the specified file name and replay the io patterns it contains. This can be used to store a workload and replay it sometime later. The iolog given may also be a blktrace binary file, which allows fio to replay a workload captured by blktrace. See blktrace for how to capture such logging data. For blktrace replay, the file needs to be turned into a blkparse binary data file first (blkparse -o /dev/null -d file_for_fio.bin). replay_no_stall=int When replaying I/O with read_iolog the default behavior is to attempt to respect the time stamps within the log and replay them with the appropriate delay between IOPS. By setting this variable fio will not respect the timestamps and attempt to replay them as fast as possible while still respecting ordering. The result is the same I/O pattern to a given device, but different timings. replay_redirect=str While replaying I/O patterns using read_iolog the default behavior is to replay the IOPS onto the major/minor device that each IOP was recorded from. This is sometimes undesirable because on a different machine those major/minor numbers can map to a different device. Changing hardware on the same system can also result in a different major/minor mapping. Replay_redirect causes all IOPS to be replayed onto the single specified device regardless of the device it was recorded from. i.e. replay_redirect=/dev/sdc would cause all IO in the blktrace or iolog to be replayed onto /dev/sdc. This means multiple devices will be replayed onto a single device, if the trace contains multiple devices. If you want multiple devices to be replayed concurrently to multiple redirected devices you must blkparse your trace into separate traces and replay them with independent fio invocations. Unfortunately this also breaks the strict time ordering between multiple device accesses. replay_align=int Force alignment of IO offsets and lengths in a trace to this power of 2 value. replay_scale=int Scale sector offsets down by this factor when replaying traces. per_job_logs=bool If set, this generates bw/clat/iops log with per file private filenames. If not set, jobs with identical names will share the log filename. Default: true. write_bw_log=str If given, write a bandwidth log of the jobs in this job file. Can be used to store data of the bandwidth of the jobs in their lifetime. The included fio_generate_plots script uses gnuplot to turn these text files into nice graphs. See write_lat_log for behaviour of given filename. For this option, the suffix is _bw.x.log, where x is the index of the job (1..N, where N is the number of jobs). If 'per_job_logs' is false, then the filename will not include the job index. See 'Log File Formats'. write_lat_log=str Same as write_bw_log, except that this option stores io submission, completion, and total latencies instead. If no filename is given with this option, the default filename of "jobname_type.log" is used. Even if the filename is given, fio will still append the type of log. So if one specifies write_lat_log=foo The actual log names will be foo_slat.x.log, foo_clat.x.log, and foo_lat.x.log, where x is the index of the job (1..N, where N is the number of jobs). This helps fio_generate_plot find the logs automatically. If 'per_job_logs' is false, then the filename will not include the job index. See 'Log File Formats'. write_hist_log=str Same as write_lat_log, but writes I/O completion latency histograms. If no filename is given with this option, the default filename of "jobname_clat_hist.x.log" is used, where x is the index of the job (1..N, where N is the number of jobs). Even if the filename is given, fio will still append the type of log. If per_job_logs is false, then the filename will not include the job index. See 'Log File Formats'. write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is given with this option, the default filename of "jobname_type.x.log" is used,where x is the index of the job (1..N, where N is the number of jobs). Even if the filename is given, fio will still append the type of log. If 'per_job_logs' is false, then the filename will not include the job index. See 'Log File Formats'. log_avg_msec=int By default, fio will log an entry in the iops, latency, or bw log for every IO that completes. When writing to the disk log, that can quickly grow to a very large size. Setting this option makes fio average the each log entry over the specified period of time, reducing the resolution of the log. See log_max_value as well. Defaults to 0, logging all entries. log_hist_msec=int Same as log_avg_msec, but logs entries for completion latency histograms. Computing latency percentiles from averages of intervals using log_avg_msec is innacurate. Setting this option makes fio log histogram entries over the specified period of time, reducing log sizes for high IOPS devices while retaining percentile accuracy. See log_hist_coarseness as well. Defaults to 0, meaning histogram logging is disabled. log_hist_coarseness=int Integer ranging from 0 to 6, defining the coarseness of the resolution of the histogram logs enabled with log_hist_msec. For each increment in coarseness, fio outputs half as many bins. Defaults to 0, for which histogram logs contain 1216 latency bins. See 'Log File Formats'. log_max_value=bool If log_avg_msec is set, fio logs the average over that window. If you instead want to log the maximum value, set this option to 1. Defaults to 0, meaning that averaged values are logged. log_offset=int If this is set, the iolog options will include the byte offset for the IO entry as well as the other data values. log_compression=int If this is set, fio will compress the IO logs as it goes, to keep the memory footprint lower. When a log reaches the specified size, that chunk is removed and compressed in the background. Given that IO logs are fairly highly compressible, this yields a nice memory savings for longer runs. The downside is that the compression will consume some background CPU cycles, so it may impact the run. This, however, is also true if the logging ends up consuming most of the system memory. So pick your poison. The IO logs are saved normally at the end of a run, by decompressing the chunks and storing them in the specified log file. This feature depends on the availability of zlib. log_compression_cpus=str Define the set of CPUs that are allowed to handle online log compression for the IO jobs. This can provide better isolation between performance sensitive jobs, and background compression work. log_store_compressed=bool If set, fio will store the log files in a compressed format. They can be decompressed with fio, using the --inflate-log command line parameter. The files will be stored with a .fz suffix. log_unix_epoch=bool If set, fio will log Unix timestamps to the log files produced by enabling write_type_log for each log type, instead of the default zero-based timestamps. block_error_percentiles=bool If set, record errors in trim block-sized units from writes and trims and output a histogram of how many trims it took to get to errors, and what kind of error was encountered. lockmem=int Pin down the specified amount of memory with mlock(2). Can potentially be used instead of removing memory or booting with less memory to simulate a smaller amount of memory. The amount specified is per worker. exec_prerun=str Before running this job, issue the command specified through system(3). Output is redirected in a file called jobname.prerun.txt. exec_postrun=str After the job completes, issue the command specified though system(3). Output is redirected in a file called jobname.postrun.txt. ioscheduler=str Attempt to switch the device hosting the file to the specified io scheduler before running. disk_util=bool Generate disk utilization statistics, if the platform supports it. Defaults to on. disable_lat=bool Disable measurements of total latency numbers. Useful only for cutting back the number of calls to gettimeofday, as that does impact performance at really high IOPS rates. Note that to really get rid of a large amount of these calls, this option must be used with disable_slat and disable_bw as well. disable_clat=bool Disable measurements of completion latency numbers. See disable_lat. disable_slat=bool Disable measurements of submission latency numbers. See disable_slat. disable_bw=bool Disable measurements of throughput/bandwidth numbers. See disable_lat. clat_percentiles=bool Enable the reporting of percentiles of completion latencies. percentile_list=float_list Overwrite the default list of percentiles for completion latencies and the block error histogram. Each number is a floating number in the range (0,100], and the maximum length of the list is 20. Use ':' to separate the numbers, and list the numbers in ascending order. For example, --percentile_list=99.5:99.9 will cause fio to report the values of completion latency below which 99.5% and 99.9% of the observed latencies fell, respectively. clocksource=str Use the given clocksource as the base of timing. The supported options are: gettimeofday gettimeofday(2) clock_gettime clock_gettime(2) cpu Internal CPU clock source cpu is the preferred clocksource if it is reliable, as it is very fast (and fio is heavy on time calls). Fio will automatically use this clocksource if it's supported and considered reliable on the system it is running on, unless another clocksource is specifically set. For x86/x86-64 CPUs, this means supporting TSC Invariant. gtod_reduce=bool Enable all of the gettimeofday() reducing options (disable_clat, disable_slat, disable_bw) plus reduce precision of the timeout somewhat to really shrink the gettimeofday() call count. With this option enabled, we only do about 0.4% of the gtod() calls we would have done if all time keeping was enabled. gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of execution to just getting the current time. Fio (and databases, for instance) are very intensive on gettimeofday() calls. With this option, you can set one CPU aside for doing nothing but logging current time to a shared memory location. Then the other threads/processes that run IO workloads need only copy that segment, instead of entering the kernel with a gettimeofday() call. The CPU set aside for doing these time calls will be excluded from other uses. Fio will manually clear it from the CPU mask of other jobs. continue_on_error=str Normally fio will exit the job on the first observed failure. If this option is set, fio will continue the job when there is a 'non-fatal error' (EIO or EILSEQ) until the runtime is exceeded or the I/O size specified is completed. If this option is used, there are two more stats that are appended, the total error count and the first error. The error field given in the stats is the first error that was hit during the run. The allowed values are: none Exit on any IO or verify errors. read Continue on read errors, exit on all others. write Continue on write errors, exit on all others. io Continue on any IO error, exit on all others. verify Continue on verify errors, exit on all others. all Continue on all errors. 0 Backward-compatible alias for 'none'. 1 Backward-compatible alias for 'all'. ignore_error=str Sometimes you want to ignore some errors during test in that case you can specify error list for each error type. ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST errors for given error type is separated with ':'. Error may be symbol ('ENOSPC', 'ENOMEM') or integer. Example: ignore_error=EAGAIN,ENOSPC:122 This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from WRITE. error_dump=bool If set dump every error even if it is non fatal, true by default. If disabled only fatal error will be dumped cgroup=str Add job to this control group. If it doesn't exist, it will be created. The system must have a mounted cgroup blkio mount point for this to work. If your system doesn't have it mounted, you can do so with: # mount -t cgroup -o blkio none /cgroup cgroup_weight=int Set the weight of the cgroup to this value. See the documentation that comes with the kernel, allowed values are in the range of 100..1000. cgroup_nodelete=bool Normally fio will delete the cgroups it has created after the job completion. To override this behavior and to leave cgroups around after the job completion, set cgroup_nodelete=1. This can be useful if one wants to inspect various cgroup files after job completion. Default: false uid=int Instead of running as the invoking user, set the user ID to this value before the thread/process does any work. gid=int Set group ID, see uid. flow_id=int The ID of the flow. If not specified, it defaults to being a global flow. See flow. flow=int Weight in token-based flow control. If this value is used, then there is a 'flow counter' which is used to regulate the proportion of activity between two or more jobs. fio attempts to keep this flow counter near zero. The 'flow' parameter stands for how much should be added or subtracted to the flow counter on each iteration of the main I/O loop. That is, if one job has flow=8 and another job has flow=-1, then there will be a roughly 1:8 ratio in how much one runs vs the other. flow_watermark=int The maximum value that the absolute value of the flow counter is allowed to reach before the job must wait for a lower value of the counter. flow_sleep=int The period of time, in microseconds, to wait after the flow watermark has been exceeded before retrying operations In addition, there are some parameters which are only valid when a specific ioengine is in use. These are used identically to normal parameters, with the caveat that when used on the command line, they must come after the ioengine that defines them is selected. [libaio] userspace_reap Normally, with the libaio engine in use, fio will use the io_getevents system call to reap newly returned events. With this flag turned on, the AIO ring will be read directly from user-space to reap events. The reaping mode is only enabled when polling for a minimum of 0 events (eg when iodepth_batch_complete=0). [psyncv2] hipri Set RWF_HIPRI on IO, indicating to the kernel that it's of higher priority than normal. [cpuio] cpuload=int Attempt to use the specified percentage of CPU cycles. [cpuio] cpuchunks=int Split the load into cycles of the given time. In microseconds. [cpuio] exit_on_io_done=bool Detect when IO threads are done, then exit. [netsplice] hostname=str [net] hostname=str The host name or IP address to use for TCP or UDP based IO. If the job is a TCP listener or UDP reader, the hostname is not used and must be omitted unless it is a valid UDP multicast address. [libhdfs] namenode=str The host name or IP address of a HDFS cluster namenode to contact. [netsplice] port=int [net] port=int The TCP or UDP port to bind to or connect to. If this is used with numjobs to spawn multiple instances of the same job type, then this will be the starting port number since fio will use a range of ports. [libhdfs] port=int the listening port of the HFDS cluster namenode. [netsplice] interface=str [net] interface=str The IP address of the network interface used to send or receive UDP multicast [netsplice] ttl=int [net] ttl=int Time-to-live value for outgoing UDP multicast packets. Default: 1 [netsplice] nodelay=bool [net] nodelay=bool Set TCP_NODELAY on TCP connections. [netsplice] protocol=str [netsplice] proto=str [net] protocol=str [net] proto=str The network protocol to use. Accepted values are: tcp Transmission control protocol tcpv6 Transmission control protocol V6 udp User datagram protocol udpv6 User datagram protocol V6 unix UNIX domain socket When the protocol is TCP or UDP, the port must also be given, as well as the hostname if the job is a TCP listener or UDP reader. For unix sockets, the normal filename option should be used and the port is invalid. [net] listen For TCP network connections, tell fio to listen for incoming connections rather than initiating an outgoing connection. The hostname must be omitted if this option is used. [net] pingpong Normally a network writer will just continue writing data, and a network reader will just consume packages. If pingpong=1 is set, a writer will send its normal payload to the reader, then wait for the reader to send the same payload back. This allows fio to measure network latencies. The submission and completion latencies then measure local time spent sending or receiving, and the completion latency measures how long it took for the other end to receive and send back. For UDP multicast traffic pingpong=1 should only be set for a single reader when multiple readers are listening to the same address. [net] window_size Set the desired socket buffer size for the connection. [net] mss Set the TCP maximum segment size (TCP_MAXSEG). [e4defrag] donorname=str File will be used as a block donor(swap extents between files) [e4defrag] inplace=int Configure donor file blocks allocation strategy 0(default): Preallocate donor's file on init 1 : allocate space immediately inside defragment event, and free right after event [rbd] clustername=str Specifies the name of the Ceph cluster. [rbd] rbdname=str Specifies the name of the RBD. [rbd] pool=str Specifies the name of the Ceph pool containing RBD. [rbd] clientname=str Specifies the username (without the 'client.' prefix) used to access the Ceph cluster. If the clustername is specified, the clientname shall be the full type.id string. If no type. prefix is given, fio will add 'client.' by default. [mtd] skip_bad=bool Skip operations against known bad blocks. [libhdfs] hdfsdirectory libhdfs will create chunk in this HDFS directory [libhdfs] chunk_size the size of the chunk to use for each file. 6.0 Interpreting the output --------------------------- fio spits out a lot of output. While running, fio will display the status of the jobs created. An example of that would be: Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s] The characters inside the square brackets denote the current status of each thread. The possible values (in typical life cycle order) are: Idle Run ---- --- P Thread setup, but not started. C Thread created. I Thread initialized, waiting or generating necessary data. p Thread running pre-reading file(s). R Running, doing sequential reads. r Running, doing random reads. W Running, doing sequential writes. w Running, doing random writes. M Running, doing mixed sequential reads/writes. m Running, doing mixed random reads/writes. F Running, currently waiting for fsync() f Running, finishing up (writing IO logs, etc) V Running, doing verification of written data. E Thread exited, not reaped by main thread yet. _ Thread reaped, or X Thread reaped, exited with an error. K Thread reaped, exited due to signal. Fio will condense the thread string as not to take up more space on the command line as is needed. For instance, if you have 10 readers and 10 writers running, the output would look like this: Jobs: 20 (f=20): [R(10),W(10)] [4.0% done] [2103MB/0KB/0KB /s] [538K/0/0 iops] [eta 57m:36s] Fio will still maintain the ordering, though. So the above means that jobs 1..10 are readers, and 11..20 are writers. The other values are fairly self explanatory - number of threads currently running and doing io, rate of io since last check (read speed listed first, then write speed), and the estimated completion percentage and time for the running group. It's impossible to estimate runtime of the following groups (if any). Note that the string is displayed in order, so it's possible to tell which of the jobs are currently doing what. The first character is the first job defined in the job file, and so forth. 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= 32MB, bw= 666KB/s, iops=89 , runt= 50320msec slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82 bw (KB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0% submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% issued r/w: total=0/32768, short=0/0 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%, lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0% The client number is printed, along with the group id and error of that thread. Below is the io statistics, here for writes. In the order listed, they denote: io= Number of megabytes io performed bw= Average bandwidth rate iops= Average IOs performed per second runt= The runtime of that thread slat= Submission latency (avg being the average, stdev being the standard deviation). This is the time it took to submit the io. For sync io, the slat is really the completion latency, since queue/complete is one operation there. This value can be in milliseconds or microseconds, fio will choose the most appropriate base and print that. In the example above, milliseconds is the best scale. Note: in --minimal mode latencies are always expressed in microseconds. 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, usage of system and user time, and finally the number of major and minor page faults. The CPU utilization numbers are averages for the jobs in that reporting group, while the context and fault counters are summed. IO depths= The distribution of io depths over the job life time. The numbers are divided into powers of 2, so for example the 16= entries includes depths up to that value but higher than the previous entry. In other words, it covers the range from 16 to 31. IO submit= How many pieces of IO were submitting in a single submit call. Each entry denotes that amount and below, until the previous entry - eg, 8=100% mean that we submitted anywhere in between 5-8 ios per submit call. IO complete= Like the above submit number, but for completions instead. IO issued= The number of read/write requests issued, and how many of them were short. IO latencies= The distribution of IO completion latencies. This is the time from when IO leaves fio and when it gets completed. The numbers follow the same pattern as the IO depths, meaning that 2=1.6% means that 1.6% of the IO completed within 2 msecs, 20=12.8% means that 12.8% of the IO took more than 10 msecs, but less than (or equal to) 20 msecs. After each client has been listed, the group statistics are printed. They will look like this: Run status group 0 (all jobs): READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec WRITE: io=64MB, 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 smallest runtime of the threads in that group. maxt= The longest runtime of the threads in that group. 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. It is also possible to get fio to dump the current output while it is running, without terminating the job. To do that, send fio the USR1 signal. You can also get regularly timed dumps by using the --status-interval parameter, or by creating a file in /tmp named fio-dump-status. If fio sees this file, it will unlink it and dump the current output status. 7.0 Terse output ---------------- For scripted usage where you typically want to generate tables or graphs of the results, fio can output the results in a semicolon separated format. The format is one long line of values, such as: 2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.446807;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00% A description of this job goes here. The job description (if provided) follows on a second line. To enable terse output, use the --minimal command line option. The first value is the version of the terse output format. If the output has to be changed for some reason, this number will be incremented by 1 to signify that change. Split up, the format is as follows: terse version, fio version, jobname, groupid, error READ status: Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec) Submission latency: min, max, mean, stdev (usec) Completion latency: min, max, mean, stdev (usec) Completion latency percentiles: 20 fields (see below) Total latency: min, max, mean, stdev (usec) Bw (KB/s): min, max, aggregate percentage of total, mean, stdev WRITE status: Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec) Submission latency: min, max, mean, stdev (usec) Completion latency: min, max, mean, stdev(usec) Completion latency percentiles: 20 fields (see below) Total latency: min, max, mean, stdev (usec) Bw (KB/s): min, max, aggregate percentage of total, mean, stdev CPU usage: user, system, context switches, major faults, minor faults IO depths: <=1, 2, 4, 8, 16, 32, >=64 IO latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000 IO latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000 Disk utilization: Disk name, Read ios, write ios, Read merges, write merges, Read ticks, write ticks, Time spent in queue, disk utilization percentage Additional Info (dependent on continue_on_error, default off): total # errors, first error code Additional Info (dependent on description being set): Text description Completion latency percentiles can be a grouping of up to 20 sets, so for the terse output fio writes all of them. Each field will look like this: 1.00%=6112 which is the Xth percentile, and the usec latency associated with it. For disk utilization, all disks used by fio are shown. So for each disk there will be a disk utilization section. 8.0 Trace file format --------------------- There are two trace file format that you can encounter. The older (v1) format is unsupported since version 1.20-rc3 (March 2008). It will still be described below in case that you get an old trace and want to understand it. In any case the trace is a simple text file with a single action per line. 8.1 Trace file format v1 ------------------------ Each line represents a single io action in the following format: rw, offset, length where rw=0/1 for read/write, and the offset and length entries being in bytes. This format is not supported in Fio versions => 1.20-rc3. 8.2 Trace file format v2 ------------------------ The second version of the trace file format was added in Fio version 1.17. It allows to access more then one file per trace and has a bigger set of possible file actions. The first line of the trace file has to be: fio version 2 iolog Following this can be lines in two different formats, which are described below. The file management format: filename action The filename is given as an absolute path. The action can be one of these: add Add the given filename to the trace open Open the file with the given filename. The filename has to have been added with the add action before. close Close the file with the given filename. The file has to have been opened before. The file io action format: filename action offset length The filename is given as an absolute path, and has to have been added and opened before it can be used with this format. The offset and length are given in bytes. The action can be one of these: wait Wait for 'offset' microseconds. Everything below 100 is discarded. The time is relative to the previous wait statement. read Read 'length' bytes beginning from 'offset' write Write 'length' bytes beginning from 'offset' sync fsync() the file datasync fdatasync() the file trim trim the given file from the given 'offset' for 'length' bytes 9.0 CPU idleness profiling -------------------------- In some cases, we want to understand CPU overhead in a test. For example, we test patches for the specific goodness of whether they reduce CPU usage. fio implements a balloon approach to create a thread per CPU that runs at idle priority, meaning that it only runs when nobody else needs the cpu. By measuring the amount of work completed by the thread, idleness of each CPU can be derived accordingly. An unit work is defined as touching a full page of unsigned characters. Mean and standard deviation of time to complete an unit work is reported in "unit work" section. Options can be chosen to report detailed percpu idleness or overall system idleness by aggregating percpu stats. 10.0 Verification and triggers ------------------------------ Fio is usually run in one of two ways, when data verification is done. The first is a normal write job of some sort with verify enabled. When the write phase has completed, fio switches to reads and verifies everything it wrote. The second model is running just the write phase, and then later on running the same job (but with reads instead of writes) to repeat the same IO patterns and verify the contents. Both of these methods depend on the write phase being completed, as fio otherwise has no idea how much data was written. With verification triggers, fio supports dumping the current write state to local files. Then a subsequent read verify workload can load this state and know exactly where to stop. This is useful for testing cases where power is cut to a server in a managed fashion, for instance. A verification trigger consists of two things: 1) Storing the write state of each job 2) Executing a trigger command The write state is relatively small, on the order of hundreds of bytes to single kilobytes. It contains information on the number of completions done, the last X completions, etc. A trigger is invoked either through creation ('touch') of a specified file in the system, or through a timeout setting. If fio is run with --trigger-file=/tmp/trigger-file, then it will continually check for the existence of /tmp/trigger-file. When it sees this file, it will fire off the trigger (thus saving state, and executing the trigger command). For client/server runs, there's both a local and remote trigger. If fio is running as a server backend, it will send the job states back to the client for safe storage, then execute the remote trigger, if specified. If a local trigger is specified, the server will still send back the write state, but the client will then execute the trigger. 10.1 Verification trigger example --------------------------------- Lets say we want to run a powercut test on the remote machine 'server'. Our write workload is in write-test.fio. We want to cut power to 'server' at some point during the run, and we'll run this test from the safety or our local machine, 'localbox'. On the server, we'll start the fio backend normally: server# fio --server and on the client, we'll fire off the workload: localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger-remote="bash -c \"echo b > /proc/sysrq-triger\"" We set /tmp/my-trigger as the trigger file, and we tell fio to execute echo b > /proc/sysrq-trigger on the server once it has received the trigger and sent us the write state. This will work, but it's not _really_ cutting power to the server, it's merely abruptly rebooting it. If we have a remote way of cutting power to the server through IPMI or similar, we could do that through a local trigger command instead. Lets assume we have a script that does IPMI reboot of a given hostname, ipmi-reboot. On localbox, we could then have run fio with a local trigger instead: localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trigger="ipmi-reboot server" For this case, fio would wait for the server to send us the write state, then execute 'ipmi-reboot server' when that happened. 10.2 Loading verify state ------------------------- To load store write state, read verification job file must contain the verify_state_load option. If that is set, fio will load the previously stored state. For a local fio run this is done by loading the files directly, and on a client/server run, the server backend will ask the client to send the files over and load them from there. 11.0 Log File Formats --------------------- Fio supports a variety of log file formats, for logging latencies, bandwidth, and IOPS. The logs share a common format, which looks like this: time (msec), value, data direction, offset Time for the log entry is always in milliseconds. The value logged depends on the type of log, it will be one of the following: Latency log Value is latency in usecs Bandwidth log Value is in KB/sec IOPS log Value is IOPS Data direction is one of the following: 0 IO is a READ 1 IO is a WRITE 2 IO is a TRIM The offset is the offset, in bytes, from the start of the file, for that particular IO. The logging of the offset can be toggled with 'log_offset'. If windowed logging is enabled through 'log_avg_msec', then fio doesn't log individual IOs. Instead of logs the average values over the specified period of time. Since 'data direction' and 'offset' are per-IO values, they aren't applicable if windowed logging is enabled. If windowed logging is enabled and 'log_max_value' is set, then fio logs maximum values in that window instead of averages.