sg_test_rwbuf - test a SCSI host adapter by issuing dummy writes and reads
or an older deprecated format sg_test_rwbuf DEVICE SZ
] [ AR
sg_test_rwbuf writes and reads back SZ
bytes to the internal buffer of
(e.g. /dev/sda or /dev/sg0). A pseudo random pattern is written
to the data buffer on the device then read back. If the same pattern is found
'Success' is reported. If they do not match (checksums unequal) then this is
reported and up to 24 bytes from the first point of mismatch are reported; the
first line shows what was written and the second line shows what was received.
For testing purposes, you can ask it to write AW
or read AR
Arguments to long options are mandatory for short options as well.
- -r, --addrd=AR
- Read an additional AR bytes (than indicated by
SZ) from the data buffer. Checksum is performed over the first
- -w, --addwr=AW
- Write an additional AW bytes (than indicated by
SZ) of zeros into the data buffer. Checksum is generated over the
first SZ bytes.
- -h, --help
- Print out a usage message the exit.
- -q, --quick
- Perform a READ BUFFER descriptor command to find out the
available data buffer length and offset, print them out then exit (without
testing with write/read sequences).
- -s, --size=SZ
- where SZ is the size of buffer in bytes to be
written then read and checked. This number needs to be less than or equal
to the size of the device's data buffer which can be seen from the
--quick option. Either this option or the --quick option
should be given.
- -t, --times=NUM
- where NUM is the number of times to repeat the
write/read to buffer test. Default value is 1 .
- -v, --verbose
- increase verbosity of output.
- -V, --version
- print version number (and data of last change) then
The microcode in a SCSI device is _not_ modified by doing a WRITE BUFFER command
with its mode set to "data" (0x2) as done by this utility. Therefore
this utility is safe in that respect. [Mode values 0x4, 0x5, 0x6 and 0x7 are
the dangerous ones :-)]
: If you access the device at the same time (e.g. because it's a
hard disk with a mounted file system on it) the device's buffer may be used by
the device itself for other data at the same time, and overwriting it may or
may not cause data corruption! HOWEVER
the SPC-3 draft standard does
state in its WRITE BUFFER command: "This command shall not alter any
medium of the logical unit when data mode ... is specified". This implies
that it _is_ safe to use this utility with devices that have mounted file
systems on them. Following this theme further, a disk with active mounted file
systems may cause the data read back to be different (due to caching activity)
to what was written and hence a checksum error.
The exit status of sg_test_rwbuf is 0 when it is successful. Otherwise see the
sg3_utils(8) man page.
Written by D. Gilbert and K. Garloff
Copyright © 2000-2012 Douglas Gilbert, Kurt Garloff
This software is distributed under the GPL version 2. There is NO warranty; not
even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.