SG_VERIFY(8)

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

SYNOPSIS
sg_verify [--bpc=<n>] [--count=<n>] [--dpo] [--help] [--lba=<n>] [--verbose] [--version] <scsi_device>

DESCRIPTION

Sends one or more SCSI VERIFY commands to the given Linux SCSI device. It is a 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=<n>' option and continues for '--count=<n>' blocks. No more than '--bpc=<n>' 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 verfy errors detected no messages are sent to stderr and the Unix return status is 0).

--bpc=<n> | -b <n>
    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 the value <n> is less than the value given to --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.

--dpo | -d
    disable page out changes the cache retension policy 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.

--count=<n> | -c <n>
    specifies the number of blocks to verify. The default value is 1 . If <n> is greater than the value associated with '--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.

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

--lba=<n> | -l <n>
    specifies the logical block address on the device to start the verify operation. The default value is 0 (i.e. the start of the device).

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

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

The arguments to --bpc, --count and --lba may be followed by one of these multiplicative suffixes: c C *1; b B *512; k *1,024; K *1,000; m *1,048,576; M *1,000,000; g *1,073,741,824; G *1,000,000,000; t *1,099,511,627,776 and T *1,000,000,000,000 (the latter two can only be used for --count and --lba).

Alternatively numerical values can be given in hexadecimal preceded by either "0x" or "0X". When hex numbers are given multipliers cannot be used.

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.

AUTHORS
Written by Douglas Gilbert.

REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT
Copyright © 2004 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)