Update size/io_size descriptions

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index c73b9ecdc859a8912718968918fe837543a258b7..8da5527a3edb6cbfd408f497260651d99c633be0 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -462,23 +462,26 @@ fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
 
 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).
-               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.
-
+               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_limit' is set to 5G, fio will perform IO within the first
-               20G but exit when 5G have been done.
+               '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
@@ -594,9 +597,12 @@ scramble_buffers=bool      If refill_buffers is too costly and the target is
 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 zeroes. 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.
+               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