sg_test_rwbuf - Tests the SCSI host adapter by issuing write and read
operations on a device’s buffer and calculating checksums.
sg_test_rwbuf [--addrd=AR] [--addwr=AW] [--help] [--quick] --size=SZ
[--times=NUM] [--verbose] [--version] DEVICE
or an older deprecated format sg_test_rwbuf DEVICE SZ [AW] [AR]
sg_test_rwbuf writes and reads back SZ bytes to the internal buffer of
DEVICE (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 additional bytes.
Arguments to long options are mandatory for short options as well.
Read an additional AR bytes (than indicated by SZ) from the data
buffer. Checksum is performed over the first SZ bytes.
Write an additional AW bytes (than indicated by SZ) of zeros
into the data buffer. Checksum is generated over the first SZ
Print out a usage message the exit.
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).
where SZis teh size of buffer in bytes to be written then read
and checked. This number needs to be less than on 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
where NUM is the number of times to repeat the write/read to
buffer test. Default value is 1 .
increase verbosity of output.
print version number (and data of last change) then exit.
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 :-)]
WARNING: 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 © 2000-2006 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