Add rw_sequencer option

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index bd5bebfc929fc1a71a09e15dba27c10d43e0a042..0ef7ca42120d175c3115207861f50b964a07958e 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -313,13 +313,30 @@ rw=str            Type of io pattern. Accepted values are:
                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
                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 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
+               a number of IO's to do before getting a new offset, this is
+               one by appending a ':<nr>' 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. See the
+               'rw_sequencer' option.
+
+rw_sequencer=str If an offset modifier is given by appending a number to
+               the rw=<str> 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
                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.
+               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
 
 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