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.