sg_test_rwbuf - Man Page

test a SCSI host adapter by issuing dummy writes and reads


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.

-r,  --addrd=AR

Read an additional AR bytes (more than indicated by SZ) from the data buffer. Checksum is performed over the first SZ bytes.

-w,  --addwr=AW

Write an additional AW bytes (more 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 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.

Exit Status

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


January 2018 sg3_utils-1.43