Add randtrimwrite data direction

[fio.git] / HOWTO.rst

diff --git a/HOWTO.rst b/HOWTO.rst
index c94238ed5b84733945cd441a70526d5b9b1c778c..e89d05f04791d22d9369aa9466b48d5e86dfc1ab 100644 (file)
--- a/HOWTO.rst
+++ b/HOWTO.rst
@@ -167,9 +167,9 @@ Command line options
        defined by `ioengine`.  If no `ioengine` is given, list all
        available ioengines.
 
-.. option:: --showcmd=jobfile
+.. option:: --showcmd
 
-       Convert `jobfile` to a set of command-line options.
+       Convert given job files to a set of command-line options.
 
 .. option:: --readonly
 
@@ -1129,7 +1129,14 @@ I/O type
                                Random mixed reads and writes.
                **trimwrite**
                                Sequential trim+write sequences. Blocks will be trimmed first,
-                               then the same blocks will be written to.
+                               then the same blocks will be written to. So if ``io_size=64K``
+                               is specified, Fio will trim a total of 64K bytes and also
+                               write 64K bytes on the same trimmed blocks. This behaviour
+                               will be consistent with ``number_ios`` or other Fio options
+                               limiting the total bytes or number of I/O's.
+               **randtrimwrite**
+                               Like trimwrite, but uses random offsets rather
+                               than sequential writes.
 
        Fio defaults to read if the option is not specified.  For the mixed I/O
        types, the default is to split them 50/50.  For certain types of I/O the
@@ -2550,7 +2557,7 @@ with the caveat that when used on the command line, they must come after the
 
    [dfs]
 
-       Specificy a different chunk size (in bytes) for the dfs file.
+       Specify a different chunk size (in bytes) for the dfs file.
        Use DAOS container's chunk size by default.
 
    [libhdfs]
@@ -2559,7 +2566,7 @@ with the caveat that when used on the command line, they must come after the
 
 .. option:: object_class=str : [dfs]
 
-       Specificy a different object class for the dfs file.
+       Specify a different object class for the dfs file.
        Use DAOS container's object class by default.
 
 .. option:: skip_bad=bool : [mtd]
@@ -3927,6 +3934,13 @@ Error handling
        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.
 
+       Note: a write error from the device may go unnoticed by fio when using
+       buffered IO, as the write() (or similar) system call merely dirties the
+       kernel pages, unless :option:`sync` or :option:`direct` is used. Device IO
+       errors occur when the dirty data is actually written out to disk. If fully
+       sync writes aren't desirable, :option:`fsync` or :option:`fdatasync` can be
+       used as well. This is specific to writes, as reads are always synchronous.
+
        The allowed values are:
 
                **none**