1SG_VERIFY(8)                       SG3_UTILS                      SG_VERIFY(8)
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NAME

6       sg_verify - invoke SCSI VERIFY command(s) on a block device
7

SYNOPSIS

9       sg_verify  [--0]  [--16]  [--bpc=BPC]  [--count=COUNT]  [--dpo]  [--ff]
10       [--ebytchk=BCH] [--group=GN] [--help] [--in=IF] [--lba=LBA] [--ndo=NDO]
11       [--quiet] [--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE
12

DESCRIPTION

14       Sends one or more SCSI VERIFY (10 or 16) commands to DEVICE. These SCSI
15       commands  are  defined  in   the   SBC-2   and   SBC-3   standards   at
16       http://www.t10.org and SBC-4 drafts.
17
18       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
28       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
41       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.
44

OPTIONS

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
50       -0, --0
51              a buffer NDO bytes long full of zeros is sent  as  the  data-out
52              part of a VERIFY command. So stdin is not read and if --in=IF is
53              given, an error is generated. Useful when BCH is 3 to  check  if
54              some or all of DEVICE (e.g. a disk) is zero filled blocks.
55
56       -S, --16
57              uses  a  VERIFY(16)  command  (default VERIFY(10)). Even without
58              this option, using an --lba=LBA which is too large,  will  cause
59              the utility to issue a VERIFY(16) command.
60
61       -b, --bpc=BPC
62              this  option  is  ignored  if  --ndo=NDO is given. Otherwise BPC
63              specifies the maximum number of blocks that will be verified  by
64              a  single  SCSI  VERIFY command. The default value is 128 blocks
65              which equates to 64 KB for a disk with 512 byte blocks.  If  BPC
66              is  less  than COUNT then multiple SCSI VERIFY commands are sent
67              to the DEVICE. For the  default  VERIFY(10)  BPC  cannot  exceed
68              0xffff   (65,535)   while   for  VERIFY(16)  BPC  cannot  exceed
69              0x7fffffff (2,147,483,647). For  recent  block  devices  (disks)
70              this  value  may  be  constrained by the maximum transfer length
71              field in the block limits VPD page.
72
73       -c, --count=COUNT
74              where COUNT specifies  the  number  of  blocks  to  verify.  The
75              default  value  is  1  .  If  COUNT  is greater than BPC (or its
76              default value of 128) and NDO is not given, 0 or less than  mul‐
77              tiple  SCSI  VERIFY  commands  are sent to the device. Otherwise
78              COUNT becomes the contents of the verification length  field  of
79              the  SCSI  VERIFY  command issued. The sg_readcap utility can be
80              used to find the maximum number of blocks that  a  block  device
81              (e.g. a disk) has.
82
83       -d, --dpo
84              disable  page out changes the cache retention priority of blocks
85              read on the device's cache to the lowest  priority.  This  means
86              that  blocks read by other commands are more likely to remain in
87              the device's cache.
88
89       -E, --ebytchk=BCH
90              sets the BYTCHK field to BCH overriding the value (1) set by the
91              --ndo=NDO  option. Values of 1, 2 or 3 are accepted for BCH how‐
92              ever sbc3r34 reserves the value 2. If this option is given  then
93              --ndo=NDO must also be given. If BCH is 3 then NDO should be the
94              size of one logical block (plus the size of some or all  of  the
95              protection information if VRP is greater than 0).
96
97       -f, --ff
98              a  buffer  NDO  bytes  long  full  of  0xff bytes is sent as the
99              data-out part of a VERIFY command. So stdin is not read  and  if
100              --in=IF is given, an error is generated. Useful when BCH is 3 to
101              check if some or all of DEVICE (e.g. a disk) is 0xff byte filled
102              blocks.
103
104       -g, --group=GN
105              where  GN  becomes the contents of the group number field in the
106              SCSI VERIFY(16) command. It can be from 0 to 63  inclusive.  The
107              default  value for GN is 0. Note that this option is ignored for
108              the SCSI VERIFY(10) command.
109
110       -h, --help
111              output the usage message then exit.
112
113       -i, --in=IF
114              where IF is the name of a file from which NDO bytes will be read
115              and  placed  in  the data-out buffer. This is only done when the
116              --ndo=NDO option is given. If this  option  is  not  given  then
117              stdin is read. If IF is "-" then stdin is also used.
118
119       -l, --lba=LBA
120              where LBA specifies the logical block address of the first block
121              to start the verify operation. LBA  is  assumed  to  be  decimal
122              unless  prefixed  by  '0x'  or  a  trailing 'h' (see below). The
123              default value is 0 (i.e. the start of the device).
124
125       -n, --ndo=NDO
126              NDO is the number of bytes  to  obtain  from  the  FN  file  (if
127              --in=FN  is  given) or from stdin. Those bytes are placed in the
128              data-out buffer associated with the SCSI VERIFY command and  NDO
129              is  placed  in  the  verification  length  field in the cdb. The
130              default value for NDO is 0 and the maximum value is dependent on
131              the OS. If the --ebytchk=BCH option is not given then the BYTCHK
132              field in the cdb is set to 1.
133
134       -q, --quiet
135              suppress the sense buffer messages associated with a  MISCOMPARE
136              sense  key that would otherwise be sent to stderr. Still set the
137              exit status to 14 which is the sense key value indicating a MIS‐
138              COMPARE .
139
140       -r, --readonly
141              opens  the  DEVICE read-only rather than read-write which is the
142              default. The Linux sg driver needs  read-write  access  for  the
143              SCSI  VERIFY  command  but  other  access  methods  may  require
144              read-only access.
145
146       -v, --verbose
147              increase the level of verbosity, (i.e. debug output).
148
149       -V, --version
150              print the version string and then exit.
151
152       -P, --vrprotect=VRP
153              where VRP is the value in the vrprotect field in the VERIFY com‐
154              mand  cdb.  It  must  be  a value between 0 and 7 inclusive. The
155              default value is zero.
156

BYTCHK

158       BYTCHK is the name of a field (two bits wide)  in  the  VERIFY(10)  and
159       VERIFY(16)  commands. When set to 1 or 3 (sbc3r34 reserves the value 2)
160       it indicates that associated with the SCSI VERIFY command,  a  data-out
161       buffer will be sent for the device (disk) to check. Using the --ndo=NDO
162       option sets the BYTCHK field to 1 and NDO is the number of bytes placed
163       in the data-out buffer. Those bytes are obtained from stdin or IF (from
164       the --in=FN option). The --ebytchk=BCH option may be used  to  override
165       the BYTCHK field value of 1 with BCH.
166
167       The calculation of NDO is left up to the user. Its value depends on the
168       logical block size (which can be found with  the  sg_readcap  utility),
169       the  COUNT  and  the VRP values. If the VRP is greater than 0 then each
170       logical block will contain an extra 8 bytes (at  least)  of  protection
171       information.
172
173       When  the  BYTCHK  field is 0 then the verification process done by the
174       device (disk) is vendor specific. It typically involves  checking  each
175       block  on  the  disk  against its error correction codes (ECC) which is
176       additional data also held on the disk.
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178       Many Operating Systems put limits on the maximum size of  the  data-out
179       (and  data-in)  buffer. For Linux at one time the limit was less than 1
180       MB but has been increased somewhat.
181

OPTION CHANGES

183       Earlier versions of this utility had a --bytchk=NDO  option  which  set
184       the  BYTCHK  bit and set the cdb verification length field to NDO.  The
185       shorter form of that option was -B NDO. For backward compatibility that
186       option  is  still  present  but  not  documented.  In  its place is the
187       --ndo=NDO whose shorter form of -n  NDO.   --ndo=NDO  sets  the  BYTCHK
188       field to 1 unless that is overridden by the --ebytchk=BCH.
189

NOTES

191       Various  numeric  arguments  (e.g. LBA) may include multiplicative suf‐
192       fixes or be given in hexadecimal. See the "NUMERIC  ARGUMENTS"  section
193       in the sg3_utils(8) man page.
194
195       The  amount  of  error  correction  and the number of retries attempted
196       before a block is considered defective are controlled in  part  by  the
197       Verify Error Recovery mode page. A note in the SBC-3 draft (rev 29 sec‐
198       tion 6.4.9 on the Verify Error Recovery mode page) advises that to min‐
199       imize  the number of checks (and hence have the most "sensitive" verify
200       check) do the following in that mode page: set the EER bit  to  0,  the
201       PER  bit  to  1,  the  DTE bit to 1, the DCR bit to 1, the verify retry
202       count to 0 and the verify recovery time limit to 0. Mode pages  can  be
203       modified with the sdparm utility.
204
205       The  SCSI  VERIFY(6)  command  defined  in the SSC-2 standard and later
206       (i.e.  for tape drive systems) is not supported by this utility.
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EXIT STATUS

209       The exit status of sg_verify is 0 when it is successful.  When  BCH  is
210       other  than  0  then  a comparison takes place and if it fails then the
211       exit status is 14 which happens to be the sense key  value  of  MISCOM‐
212       PARE.   Otherwise  see  the EXIT STATUS section in the sg3_utils(8) man
213       page.
214
215       Earlier versions of this utility set an exit status of  98  when  there
216       was a MISCOMPARE.
217

AUTHORS

219       Written by Douglas Gilbert.
220

REPORTING BUGS

222       Report bugs to <dgilbert at interlog dot com>.
223
225       Copyright © 2004-2019 Douglas Gilbert
226       This  software is distributed under a FreeBSD license. There is NO war‐
227       ranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR  PUR‐
228       POSE.
229

SEE ALSO

231       sdparm(sdparm),       sg_modes(sg3_utils),       sg_readcap(sg3_utils),
232       sg_inq(sg3_utils)
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236sg3_utils-1.45                   December 2019                    SG_VERIFY(8)
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