xfs_scrub: optionally use SCSI READ VERIFY commands to scrub data blocks on disk

xfs_scrub: optionally use SCSI READ VERIFY commands to scrub data blocks on disk

If we sense that we're talking to a raw SCSI disk, use the SCSI READ
VERIFY command to ask the disk to verify a disk internally.  This can
sharply reduce the runtime of the data block verification phase on
devices whose internal bandwidth exceeds their link bandwidth.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>