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]  [--verbose]
       [--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  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.

OPTIONS

       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.

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 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.

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  MERCHANTABILITY
       or FITNESS FOR A PARTICULAR PURPOSE.