1SG_VERIFY(8) SG3_UTILS SG_VERIFY(8)
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6 sg_verify - invoke SCSI VERIFY command(s) on a block device
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9 sg_verify [--16] [--bpc=BPC] [--count=COUNT] [--dpo] [--ebytchk=BCH]
10 [--group=GN] [--help] [--in=IF] [--lba=LBA] [--ndo=NDO] [--quiet]
11 [--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE
12
14 Sends one or more SCSI VERIFY (10 or 16) commands to DEVICE. These SCSI
15 commands are defined in the SBC-2 (draft) standard at
16 http://www.t10.org and SBC-3 drafts.
17 When --ndo=NDO is not given then the verify starts at the logical block
19 address given by the --lba=LBA option and continues for --count=COUNT
20 blocks. No more than --bpc=BPC blocks are verified by each VERIFY com‐
21 mand so if necessary multiple VERIFY commands are sent. Medium verifi‐
22 cation operations are performed by the DEVICE (e.g. assuming each
23 block has additional EEC data, check this against the logical block
24 contents). No news is good news (i.e. if there are no verify errors
25 detected then no messages are sent to stderr and the Unix exit status
26 is 0).
27 When --ndo=NDO is given then the --bpc=BPC option is ignored. A single
29 VERIFY command is issued and a comparison starts at the logical block
30 address given by the --lba=LBA option and continues for --count=COUNT
31 blocks. The VERIFY command has an associated data-out buffer that is
32 NDO bytes long. The contents of the data-out buffer are obtained from
33 the FN file (if --in=FN is given) or from stdin. A comparison takes
34 place between data-out buffer and the logical blocks on the DEVICE. If
35 the comparison is good then no messages are sent to stderr and the Unix
36 exit status is 0. If the comparison fails then a sense buffer with a
37 sense key of MISCOMPARE is returned; in this case the Unix exit status
38 will be 14. Messages will be sent to stderr associated with MISCOMPARE
39 sense buffer unless the --quiet option is given.
40 In SBC-3 revision 34 the BYTCHK field in all SCSI VERIFY commands was
42 expanded from one to two bits. That required some changes in the
43 options of this utility, see the section below on OPTION CHANGES.
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46 Arguments to long options are mandatory for short options as well. The
47 options are arranged in alphabetical order based on the long option
48 name.
49 -S, --16
51 uses a VERIFY(16) command (default VERIFY(10)). Even without
52 this option, using an --lba=LBA which is too large, will cause
53 the utility to issue a VERIFY(16) command.
54 -b, --bpc=BPC
56 this option is ignored if --ndo=NDO is given. Otherwise BPC
57 specifies the maximum number of blocks that will be verified by
58 a single SCSI VERIFY command. The default value is 128 blocks
59 which equates to 64 KB for a disk with 512 byte blocks. If BPC
60 is less than COUNT then multiple SCSI VERIFY commands are sent
61 to the DEVICE. For the default VERIFY(10) BPC cannot exceed
62 0xffff (65,535) while for VERIFY(16) BPC cannot exceed
63 0x7fffffff (2,147,483,647). For recent block devices (disks)
64 this value may be constrained by the maximum transfer length
65 field in the block limits VPD page.
66 -c, --count=COUNT
68 where COUNT specifies the number of blocks to verify. The
69 default value is 1 . If COUNT is greater than BPC (or its
70 default value of 128) and NDO is not given, 0 or less then mul‐
71 tiple SCSI VERIFY commands are sent to the device. Otherwise
72 COUNT becomes the contents of the verification length field of
73 the SCSI VERIFY command issued. The sg_readcap utility can be
74 used to find the maximum number of blocks that a block device
75 (e.g. a disk) has.
76 -d, --dpo
78 disable page out changes the cache retention priority of blocks
79 read on the device's cache to the lowest priority. This means
80 that blocks read by other commands are more likely to remain in
81 the device's cache.
82 -E, --ebytchk=BCH
84 sets the BYTCHK field to BCH overriding the value (1) set by the
85 --ndo=NDO option. Values of 1, 2 or 3 are accepted for BCH how‐
86 ever sbc3r34 reserves the value 2. If this option is given then
87 --ndo=NDO must also be given. If BCH is 3 then COUNT must be 1
88 and NDO should be the size of one logical block (plus the size
89 of some or all of the protection infomation if VRP is greater
90 than 0).
91 -g, --group=GN
93 where GN becomes the contents of the group number field in the
94 SCSI VERIFY(16) command. The default value for GN is 0. Note
95 that this option is ignored for the SCSI VERIFY(10) command.
96 -h, --help
98 output the usage message then exit.
99 -i, --in=IF
101 where IF is the name of a file from which NDO bytes will be read
102 and placed in the data-out buffer. This is only done when the
103 --ndo=NDO option is given. If this option is not given then
104 stdin is read. If IF is "-" then stdin is also used.
105 -l, --lba=LBA
107 where LBA specifies the logical block address of the first block
108 to start the verify operation. LBA is assumed to be decimal
109 unless prefixed by '0x' or a trailing 'h' (see below). The
110 default value is 0 (i.e. the start of the device).
111 -n, --ndo=NDO
113 NDO is the number of bytes to obtain from the FN file (if
114 --in=FN is given) or from stdin. Those bytes are placed in the
115 data-out buffer associated with the SCSI VERIFY command and NDO
116 is placed in the verification length field in the cdb. The
117 default value for NDO is 0 and the maximum value is dependant on
118 the OS. If the --ebytchk=BCH option is not given then the BYTCHK
119 field in the cdb is set to 1.
120 -q, --quiet
122 suppress the sense buffer messages associated with a MISCOMPARE
123 sense key that would otherwise be sent to stderr. Still set the
124 exit status to 14 which is the sense key value indicating a MIS‐
125 COMPARE .
126 -r, --readonly
128 opens the DEVICE read-only rather than read-write which is the
129 default. The Linux sg driver needs read-write access for the
130 SCSI VERIFY command but other access methods may require
131 read-only access.
132 -v, --verbose
134 increase the level of verbosity, (i.e. debug output).
135 -V, --version
137 print the version string and then exit.
138 -P, --vrprotect=VRP
140 where VRP is the value in the vrprotect field in the VERIFY com‐
141 mand cdb. It must be a value between 0 and 7 inclusive. The
142 default value is zero.
143
145 BYTCHK is the name of a field (two bits wide) in the VERIFY(10) and
146 VERIFY(16) commands. When set to 1 or 3 (sbc3r34 reserves the value 2)
147 it indicates that associated with the SCSI VERIFY command, a data-out
148 buffer will be sent for the device (disk) to check. Using the --ndo=NDO
149 option sets the BYTCHK field to 1 and NDO is the number of bytes placed
150 in the data-out buffer. Those bytes are obtained from stdin or IF (from
151 the --in=FN option). The --ebytchk=BCH option may be used to override
152 the BYTCHK field value of 1 with BCH.
153 The calculation of NDO is left up to the user. Its value depends on the
155 logical block size (which can be found with the sg_readcap utility),
156 the COUNT and the VRP values. If the VRP is greater than 0 then each
157 logical block will contain an extra 8 bytes (at least) of protection
158 information.
159 When the BYTCHK field is 0 then the verification process done by the
161 device (disk) is vendor specific. It typically involves checking each
162 block on the disk against its error correction codes (ECC) which is
163 additional data also held on the disk.
164 Many Operating Systems put limits on the maximum size of the data-out
166 (and data-in) buffer. For Linux at one time the limit was less than 1
167 MB but has been increased somewhat.
168
170 Earlier versions of this utility had a --bytchk=NDO option which set
171 the BYTCHK bit and set the cdb verification length field to NDO. The
172 shorter form of that option was -B NDO. For backward compatibility that
173 option is still present but not documented. In its place is the
174 --ndo=NDO whose shorter form of -n NDO. --ndo=NDO sets the BYTCHK
175 field to 1 unless that is overridden by the --ebytchk=BCH.
176
178 Various numeric arguments (e.g. LBA) may include multiplicative suf‐
179 fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
180 in the sg3_utils(8) man page.
181 The amount of error correction and the number of retries attempted
183 before a block is considered defective are controlled in part by the
184 Verify Error Recovery mode page. A note in the SBC-3 draft (rev 29 sec‐
185 tion 6.4.9 on the Verify Error Recovery mode page) advises that to min‐
186 imize the number of checks (and hence have the most "sensitive" verify
187 check) do the following in that mode page: set the EER bit to 0, the
188 PER bit to 1, the DTE bit to 1, the DCR bit to 1, the verify retry
189 count to 0 and the verify recovery time limit to 0. Mode pages can be
190 modified with the sdparm utility.
191 The SCSI VERIFY(6) command defined in the SSC-2 standard and later
193 (i.e. for tape drive systems) is not supported by this utility.
194
196 The exit status of sg_verify is 0 when it is successful. When BCH is
197 other than 0 then a comparison takes place and if it fails then the
198 exit status is 14 which happens to be the sense key value of MISCOM‐
199 PARE. Otherwise see the EXIT STATUS section in the sg3_utils(8) man
200 page.
201 Earlier versions of this utility set an exit status of 98 when there
203 was a MISCOMPARE.
204
206 Written by Douglas Gilbert.
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209 Report bugs to <dgilbert at interlog dot com>.
210
212 Copyright © 2004-2013 Douglas Gilbert
213 This software is distributed under a FreeBSD license. There is NO war‐
214 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
215 POSE.
216
218 sdparm(sdparm), sg_modes(sg3_utils), sg_readcap(sg3_utils),
219 sg_inq(sg3_utils)
220sg3_utils-1.37 August 2013 SG_VERIFY(8)