# phpman > man > sg_test_rwbuf(8) [SG_TEST_RWBUF(8)](https://www.chedong.com/phpMan.php/man/SGTESTRWBUF/8/markdown) SG3_UTILS [SG_TEST_RWBUF(8)](https://www.chedong.com/phpMan.php/man/SGTESTRWBUF/8/markdown) ## NAME sg_test_rwbuf - test a SCSI host adapter by issuing dummy writes and reads ## SYNOPSIS **sg**___**test**___**rwbuf** [_--addrd=AR_] [_--addwr=AW_] [_--help_] [_--quick_] _--size=SZ_ [_--times=NUM_] [_--ver__‐ _bose_] [_--version_] _DEVICE_ or an older deprecated format **sg**___**test**___**rwbuf** _DEVICE_ _SZ_ [_AW_] [_AR_] ## DESCRIPTION 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 un‐ equal) then this is reported and up to 24 bytes from the first point of mismatch are re‐ ported; 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. ## OPTIONS Arguments to long options are mandatory for short options as well. ### -r --addrd Read an additional _AR_ bytes (more than indicated by _SZ_) from the data buffer. Checksum is performed over the first _SZ_ bytes. ### -w --addwr Write an additional _AW_ bytes (more than indicated by _SZ_) of zeros into the data buf‐ fer. 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 where _SZ_ is the size of buffer in bytes to be written then read and checked. This num‐ ber 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 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. ## NOTES 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 re‐ spect. [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)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) man page. ## AUTHORS Written by D. Gilbert and K. Garloff ## COPYRIGHT Copyright © 2000-2018 Douglas Gilbert, Kurt Garloff This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐ CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. sg3_utils-1.43 January 2018 [SG_TEST_RWBUF(8)](https://www.chedong.com/phpMan.php/man/SGTESTRWBUF/8/markdown)