SG_TEST_RWBUFSection: SG3_UTILS (8)Updated: November 2003 |
NAME
sg_test_rwbuf - Tests the SCSI host adapter by issueing write and read operations on a device's buffer and calculating checksums.SYNOPSIS
sg_test_rwbuf <generic device> <sz> [addwr] [addrd]DESCRIPTION
sg_test_rwbuf writes and reads back sz bytes to the internal buffer of device <generic device> (e.g. /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 (addwr) or read (addrd) additional bytes.
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 mounted hard disk, 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.
AUTHORS
Written by D. Gilbert and K. GarloffCOPYRIGHT
Copyright © 2000-2003 Douglas Gilbert, Kurt GarloffThis software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.