sg_verify man page on SuSE
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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] [--bytchk=NDO] [--count=COUNT] [--dpo]
[--ebytchk=BVAL] [--group=GN] [--help] [--in=IF] [--lba=LBA] [--read‐
only] [--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 sin‐
gle 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 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=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, --read‐
only 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
--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 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. 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 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-1.35 December 2012 SG_VERIFY(8)
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