Go to main content

man pages section 8: System Administration Commands

Exit Print View

Updated: Thursday, June 13, 2019

sg_verify (8)


sg_verify - invoke SCSI VERIFY command(s) on a block device


sg_verify  [--16]  [--bpc=BPC]  [--count=COUNT] [--dpo] [--ebytchk=BCH]
[--group=GN]  [--help]  [--in=IF]  [--lba=LBA]  [--ndo=NDO]   [--quiet]
[--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE


SG_VERIFY(8)                       SG3_UTILS                      SG_VERIFY(8)

       sg_verify - invoke SCSI VERIFY command(s) on a block device

       sg_verify  [--16]  [--bpc=BPC]  [--count=COUNT] [--dpo] [--ebytchk=BCH]
       [--group=GN]  [--help]  [--in=IF]  [--lba=LBA]  [--ndo=NDO]   [--quiet]
       [--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE

       Sends one or more SCSI VERIFY (10 or 16) commands to DEVICE. These SCSI
       commands   are   defined   in   the   SBC-2   (draft)    standard    at
       http://www.t10.org and SBC-3 drafts.

       When --ndo=NDO is not given then the verify starts at the logical block
       address given by the --lba=LBA option and continues  for  --count=COUNT
       blocks.  No more than --bpc=BPC blocks are verified by each VERIFY com-
       mand so if necessary multiple VERIFY commands are sent. Medium  verifi-
       cation  operations  are  performed  by  the DEVICE (e.g.  assuming each
       block has additional EEC data, check this  against  the  logical  block
       contents).  No  news  is  good news (i.e. if there are no verify errors
       detected then no messages are sent to stderr and the Unix  exit  status
       is 0).

       When  --ndo=NDO is given then the --bpc=BPC option is ignored. A single
       VERIFY command is issued and a comparison starts at the  logical  block
       address  given  by the --lba=LBA option and continues for --count=COUNT
       blocks. The VERIFY command has an associated data-out  buffer  that  is
       NDO  bytes  long. The contents of the data-out buffer are obtained from
       the FN file (if --in=FN is given) or from stdin.   A  comparison  takes
       place  between data-out buffer and the logical blocks on the DEVICE. If
       the comparison is good then no messages are sent to stderr and the Unix
       exit  status  is  0. If the comparison fails then a sense buffer with a
       sense key of MISCOMPARE is returned; in this case the Unix exit  status
       will  be 14. Messages will be sent to stderr associated with MISCOMPARE
       sense buffer unless the --quiet option is given.

       In SBC-3 revision 34 the BYTCHK field in all SCSI VERIFY  commands  was
       expanded  from  one  to  two  bits.  That  required some changes in the
       options of this utility, see the section below on OPTION CHANGES.

       Arguments to long options are mandatory for short options as well.  The
       options  are  arranged  in  alphabetical order based on the long option

       -S, --16
              uses a VERIFY(16) command  (default  VERIFY(10)).  Even  without
              this  option,  using an --lba=LBA which is too large, will cause
              the utility to issue a VERIFY(16) command.

       -b, --bpc=BPC
              this option is ignored if  --ndo=NDO  is  given.  Otherwise  BPC
              specifies  the maximum number of blocks that will be verified by
              a single SCSI VERIFY command. The default value  is  128  blocks
              which  equates  to 64 KB for a disk with 512 byte blocks. If BPC
              is less than COUNT then multiple SCSI VERIFY commands  are  sent
              to  the  DEVICE.  For  the  default VERIFY(10) BPC cannot exceed
              0xffff  (65,535)  while  for  VERIFY(16)   BPC   cannot   exceed
              0x7fffffff  (2,147,483,647).  For  recent  block devices (disks)
              this value may be constrained by  the  maximum  transfer  length
              field in the block limits VPD page.

       -c, --count=COUNT
              where  COUNT  specifies  the  number  of  blocks  to verify. The
              default value is 1 . If  COUNT  is  greater  than  BPC  (or  its
              default  value of 128) and NDO is not given, 0 or less then mul-
              tiple SCSI VERIFY commands are sent  to  the  device.  Otherwise
              COUNT  becomes  the contents of the verification length field of
              the SCSI VERIFY command issued. The sg_readcap  utility  can  be
              used  to  find  the maximum number of blocks that a block device
              (e.g. a disk) has.

       -d, --dpo
              disable page out changes the cache retention priority of  blocks
              read  on  the  device's cache to the lowest priority. This means
              that blocks read by other commands are more likely to remain  in
              the device's cache.

       -E, --ebytchk=BCH
              sets the BYTCHK field to BCH overriding the value (1) set by the
              --ndo=NDO option. Values of 1, 2 or 3 are accepted for BCH  how-
              ever  sbc3r34 reserves the value 2. If this option is given then
              --ndo=NDO must also be given. If BCH is 3 then COUNT must  be  1
              and  NDO  should be the size of one logical block (plus the size
              of some or all of the protection infomation if  VRP  is  greater
              than 0).

       -g, --group=GN
              where  GN  becomes the contents of the group number field in the
              SCSI VERIFY(16) command. The default value for  GN  is  0.  Note
              that this option is ignored for the SCSI VERIFY(10) command.

       -h, --help
              output the usage message then exit.

       -i, --in=IF
              where IF is the name of a file from which NDO bytes will be read
              and placed in the data-out buffer. This is only  done  when  the
              --ndo=NDO  option  is  given.  If  this option is not given then
              stdin is read. If IF is "-" then stdin is also used.

       -l, --lba=LBA
              where LBA specifies the logical block address of the first block
              to  start  the  verify  operation.  LBA is assumed to be decimal
              unless prefixed by '0x' or  a  trailing  'h'  (see  below).  The
              default value is 0 (i.e. the start of the device).

       -n, --ndo=NDO
              NDO  is  the  number  of  bytes  to  obtain from the FN file (if
              --in=FN is given) or from stdin. Those bytes are placed  in  the
              data-out  buffer associated with the SCSI VERIFY command and NDO
              is placed in the verification  length  field  in  the  cdb.  The
              default value for NDO is 0 and the maximum value is dependant on
              the OS. If the --ebytchk=BCH option is not given then the BYTCHK
              field in the cdb is set to 1.

       -q, --quiet
              suppress  the sense buffer messages associated with a MISCOMPARE
              sense key that would otherwise be sent to stderr. Still set  the
              exit status to 14 which is the sense key value indicating a MIS-
              COMPARE .

       -r, --readonly
              opens the DEVICE read-only rather than read-write which  is  the
              default.  The  Linux  sg  driver needs read-write access for the
              SCSI  VERIFY  command  but  other  access  methods  may  require
              read-only access.

       -v, --verbose
              increase the level of verbosity, (i.e. debug output).

       -V, --version
              print the version string and then exit.

       -P, --vrprotect=VRP
              where VRP is the value in the vrprotect field in the VERIFY com-
              mand cdb. It must be a value between  0  and  7  inclusive.  The
              default value is zero.

       BYTCHK  is  the  name  of a field (two bits wide) in the VERIFY(10) and
       VERIFY(16) commands. When set to 1 or 3 (sbc3r34 reserves the value  2)
       it  indicates  that associated with the SCSI VERIFY command, a data-out
       buffer will be sent for the device (disk) to check. Using the --ndo=NDO
       option sets the BYTCHK field to 1 and NDO is the number of bytes placed
       in the data-out buffer. Those bytes are obtained from stdin or IF (from
       the  --in=FN  option). The --ebytchk=BCH option may be used to override
       the BYTCHK field value of 1 with BCH.

       The calculation of NDO is left up to the user. Its value depends on the
       logical  block  size  (which can be found with the sg_readcap utility),
       the COUNT and the VRP values. If the VRP is greater than  0  then  each
       logical  block  will  contain an extra 8 bytes (at least) of protection

       When the BYTCHK field is 0 then the verification process  done  by  the
       device  (disk)  is vendor specific. It typically involves checking each
       block on the disk against its error correction  codes  (ECC)  which  is
       additional data also held on the disk.

       Many  Operating  Systems put limits on the maximum size of the data-out
       (and data-in) buffer. For Linux at one time the limit was less  than  1
       MB but has been increased somewhat.

       Earlier  versions  of  this utility had a --bytchk=NDO option which set
       the BYTCHK bit and set the cdb verification length field to  NDO.   The
       shorter form of that option was -B NDO. For backward compatibility that
       option is still present  but  not  documented.  In  its  place  is  the
       --ndo=NDO  whose  shorter  form  of  -n NDO.  --ndo=NDO sets the BYTCHK
       field to 1 unless that is overridden by the --ebytchk=BCH.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | system/storage/sg3_utils |
       |Stability      | Pass-through uncommitted |
       Various numeric arguments (e.g. LBA) may  include  multiplicative  suf-
       fixes  or  be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
       in the sg3_utils(8) man page.

       The amount of error correction and  the  number  of  retries  attempted
       before  a  block  is considered defective are controlled in part by the
       Verify Error Recovery mode page. A note in the SBC-3 draft (rev 29 sec-
       tion 6.4.9 on the Verify Error Recovery mode page) advises that to min-
       imize the number of checks (and hence have the most "sensitive"  verify
       check)  do  the  following in that mode page: set the EER bit to 0, the
       PER bit to 1, the DTE bit to 1, the DCR bit  to  1,  the  verify  retry
       count  to  0 and the verify recovery time limit to 0. Mode pages can be
       modified with the sdparm utility.

       The SCSI VERIFY(6) command defined in  the  SSC-2  standard  and  later
       (i.e.  for tape drive systems) is not supported by this utility.

       The  exit  status  of sg_verify is 0 when it is successful. When BCH is
       other than 0 then a comparison takes place and if  it  fails  then  the
       exit  status  is  14 which happens to be the sense key value of MISCOM-
       PARE.  Otherwise see the EXIT STATUS section in  the  sg3_utils(8)  man

       Earlier  versions  of  this utility set an exit status of 98 when there
       was a MISCOMPARE.

       Written by Douglas Gilbert.

       Report bugs to <dgilbert at interlog dot com>.

       Copyright (C) 2004-2013 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO  war-
       ranty;  not  even  for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR-

       sdparm(sdparm),       sg_modes(sg3_utils),       sg_readcap(sg3_utils),

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://sg.danny.cz/sg/p/sg3_utils-1.42.tgz

       Further information about this software can be found on the open source
       community website at http://sg.danny.cz/sg/sg3_utils.html.

sg3_utils-1.37                    August 2013                     SG_VERIFY(8)