or an older deprecated format
sg_test_rwbufDEVICESZ [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 bytes.
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 be given.
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.