SG_VERIFY(8)

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

SYNOPSIS
sg_verify [--bpc=BPC] [--count=COUNT] [--dpo] [--help] [--lba=LBA] [--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE

DESCRIPTION

Sends one or more SCSI VERIFY commands to DEVICE. It is the 10 byte VERIFY command defined for block devices (see SBC-2 at http://www.t10.org). 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 no messages are sent to stderr and the Unix return status is 0).

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.

-b, --bpc=BPC
    where 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 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) then multiple SCSI VERIFY commands are sent to the device. 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.

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

-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.

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-2 (draft) standard 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 error recovery timeout to 0. Mode pages can be modified with the sginfo 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 © 2004-2011 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
sginfo(sg3_utils), sg_modes(sg3_utils), sg_readcap(sg3_utils), sg_inq(sg3_utils)