Usage: sg_compare_and_write [--dpo] [--fua] [--fua_nv] [--grpnum=GN] [--help]
                            --in=IF|--inc=IF [--inw=WF] --lba=LBA [--num=NUM]
                            [--quiet] [--timeout=TO] [--verbose] [--version]
                            [--wrprotect=WP] [--xferlen=LEN] DEVICE
  where:
    --dpo|-d            set the dpo bit in cdb (def: clear)
    --fua|-f            set the fua bit in cdb (def: clear)
    --fua_nv|-F         set the fua_nv bit in cdb (def: clear)
    --grpnum=GN|-g GN    GN is GROUP NUMBER to set in cdb (def: 0)
    --help|-h           print out usage message
    --in=IF|-i IF       IF is a file containing a compare buffer and
                        optionally a write buffer (when --inw=WF is
                        not given)
    --inc=IF|-C IF      The same as the --in option
    --inw=WF|-D WF      WF is a file containing a write buffer
    --lba=LBA|-l LBA    LBA of the first block to compare and write
    --num=NUM|-n NUM    number of blocks to compare/write (def: 1)
    --quiet|-q          suppress MISCOMPARE report to stderr,
                        still sets exit status of 14
    --timeout=TO|-t TO    timeout for the command (def: 60 secs)
    --verbose|-v        increase verbosity (use '-vv' for more)
    --version|-V        print version string then exit
    --wrprotect=WP|-w WP    write protect information (def: 0)
    --xferlen=LEN|-x LEN    number of bytes to transfer. Default is
                            (2 * NUM * 512) or 1024 when NUM is 1

Performs a SCSI COMPARE AND WRITE operation. Sends a double size
buffer, the first half is used to compare what is at LBA for NUM
blocks. If and only if the comparison is equal, then the second
half of the buffer is written to LBA for NUM blocks.