sg_verify man page on Alpinelinux
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SG_VERIFY(8) SG3_UTILS SG_VERIFY(8)
NAME
sg_verify - invoke SCSI VERIFY command(s) on a block device
SYNOPSIS
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
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 --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.
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 --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
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
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.
OPTION CHANGES
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.
NOTES
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.
EXIT STATUS
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
page.
Earlier versions of this utility set an exit status of 98 when there
was a MISCOMPARE.
AUTHORS
Written by Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 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‐
POSE.
SEE ALSO
sdparm(sdparm), sg_modes(sg3_utils), sg_readcap(sg3_utils),
sg_inq(sg3_utils)
sg3_utils-1.37 August 2013 SG_VERIFY(8)
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