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

Provided by: sg3-utils_1.36-1ubuntu1_amd64

NAME

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

SYNOPSIS

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

DESCRIPTION

       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 --bytchk=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 command so if necessary multiple  VERIFY  commands  are
       sent.  No  news is good news (i.e. if there are no verify errors detected then no messages
       are sent to stderr and the Unix return status is 0).

       When --bytchk=NDO is given then the --bpc=BPC option is ignored. A single  verify  command
       is  issued  and  it  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.

OPTIONS

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

-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 --bytchk=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.

-B, --bytchk=NDO
sets the BYTCHK field to one in the VERIFY command. 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. The minimum value
for NDO is 1 and the maximum value is dependant on the OS. The actual value in the
BYTCHK field in the VERIFY command may be modified by a --ebytchk=BVAL option.

-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 multiple 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=BVAL
sets the BYTCHK field to BVAL overriding the value (1) set by the --bytchk=NDO
option. Values of 1, 2 or 3 are accepted for BVAL however sbc3r34 reserves the
value 2. If this option is given then --bytchk=NDO must also be given. If BVAL 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 --bytchk=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).
-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 command cdb. It must be
a value between 0 and 7 inclusive. The default value is zero.

BYTCHK

       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  --bytchk=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=BVAL  option  may be used to override the BYTCHK field value of 1
       with BVAL.

       The calculation of NDO is left up to the user. Its value depends on the logical block size
       (which cab 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 information.

       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.

NOTES

       Various  numeric  arguments  (e.g. LBA) may include multiplicative suffixes 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 section 6.4.9 on the Verify Error Recovery mode  page)  advises
       that  to  minimize 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.

EXIT STATUS

       The  exit  status  of sg_verify is 0 when it is successful. Otherwise see the sg3_utils(8)
       man page.

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2004-2012 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not  even  for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.