docs: add documentation for sg ioengine WRITE SAME, WRITE AND VERIFY command support

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index d200700961c91174c1f0075eccd6a3ee0eb29ce8..7680f9c7634a7e55044dba0a8ebdc6928fb3bfc0 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -2079,6 +2079,26 @@ with the caveat that when used on the command line, they must come after the
        With writefua option set to 1, write operations include
        the force unit access (fua) flag. Default is 0.
 
+.. option:: sg_write_mode=str : [sg]
+       Specify the type of write commands to issue. This option can take three values:
+
+       **write**
+               This is the default where write opcodes are issued as usual.
+       **verify**
+               Issue WRITE AND VERIFY commands. The BYTCHK bit is set to 0. This
+               directs the device to carry out a medium verification with no data
+               comparison. The writefua option is ignored with this selection.
+       **same**
+               Issue WRITE SAME commands. This transfers a single block to the device
+               and writes this same block of data to a contiguous sequence of LBAs
+               beginning at the specified offset. fio's block size parameter specifies
+               the amount of data written with each command. However, the amount of data
+               actually transferred to the device is equal to the device's block
+               (sector) size. For a device with 512 byte sectors, blocksize=8k will
+               write 16 sectors with each command. fio will still generate 8k of data
+               for each command but only the first 512 bytes will be used and
+               transferred to the device. The writefua option is ignored with this
+               selection.
 
 I/O depth
 ~~~~~~~~~