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  [--16]  [--bpc=BPC]  [--count=COUNT] [--dpo] [--ebytchk=BCH]
10       [--group=GN]  [--help]  [--in=IF]  [--lba=LBA]  [--nbo=NBO]   [--quiet]
11       [--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   (draft)    standard    at
16       http://www.t10.org and SBC-3 drafts.
17
18       When --nbo=NBO 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  --nbo=NBO 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       NBO  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       -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
55       -b, --bpc=BPC
56              this option is ignored if  --nbo=NBO  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
67       -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 NBO 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
77       -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
83       -E, --ebytchk=BCH
84              sets the BYTCHK field to BCH overriding the value (1) set by the
85              --nbo=NBO 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              --nbo=NBO must also be given. If BCH is 3 then COUNT must  be  1
88              and  NBO  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
92       -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
97       -h, --help
98              output the usage message then exit.
99
100       -i, --in=IF
101              where IF is the name of a file from which NBO bytes will be read
102              and placed in the data-out buffer. This is only  done  when  the
103              --nbo=NBO  option  is  given.  If  this option is not given then
104              stdin is read. If IF is "-" then stdin is also used.
105
106       -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
112       -n, --nbo=NBO
113              NBO  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 NBO
116              is placed in the verification  length  field  in  the  cdb.  The
117              default value for NBO 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
121       -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
127       -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
133       -v, --verbose
134              increase the level of verbosity, (i.e. debug output).
135
136       -V, --version
137              print the version string and then exit.
138
139       -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

BYTCHK

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 --nbo=NBO
149       option sets the BYTCHK field to 1 and NBO 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
154       The calculation of NBO 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
160       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
165       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

OPTION CHANGES

170       Earlier  versions  of  this utility had a --bytchk=NBO option which set
171       the BYTCHK bit and set the cdb verification length field to  NBO.   The
172       shorter form of that option was -B NBO. For backward compatibility that
173       option is still present  but  not  documented.  In  its  place  is  the
174       --nbo=NBO  whose  shorter  form  of  -n NBO.  --nbo=NBO sets the BYTCHK
175       field to 1 unless that is overridden by the --ebytchk=BCH.
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NOTES

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
182       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
192       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

EXIT STATUS

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
202       Earlier  versions  of  this utility set an exit status of 98 when there
203       was a MISCOMPARE.
204

AUTHORS

206       Written by Douglas Gilbert.
207

REPORTING BUGS

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

SEE ALSO

218       sdparm(sdparm),       sg_modes(sg3_utils),       sg_readcap(sg3_utils),
219       sg_inq(sg3_utils)
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223sg3_utils-1.37                    August 2013                     SG_VERIFY(8)
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