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man pages section 8: System Administration Commands

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Updated: Thursday, June 13, 2019

sg_write_verify (8)


sg_write_verify - send the SCSI WRITE AND VERIFY command


sg_write_verify  [--16]  [--bytchk=BC]  [--dpo]  [--group=GN]  [--help]
[--ilen=ILEN] [--in=IF] --lba=LBA [--num=NUM] [--repeat] [--timeout=TO]
[--verbose] [--version] [--wrprotect=WP] DEVICE


WRITE AND VERIFY(8)                SG3_UTILS               WRITE AND VERIFY(8)

       sg_write_and_verify - send the SCSI WRITE AND VERIFY command

       sg_write_verify  [--16]  [--bytchk=BC]  [--dpo]  [--group=GN]  [--help]
       [--ilen=ILEN] [--in=IF] --lba=LBA [--num=NUM] [--repeat] [--timeout=TO]
       [--verbose] [--version] [--wrprotect=WP] DEVICE

       Send  a  SCSI WRITE AND VERIFY (10) or (16) command to DEVICE. The data
       to be written is read from the IF file or, in  its  absence,  a  buffer
       full of 0xff bytes is used. The length of the data-out buffer sent with
       the command is ILEN bytes or, if that is not  given,  then  it  is  the
       length of the IF file.

       The write operation is to the DEVICE's medium (optionally to its cache)
       starting at logical block address LBA for NUM  logical  blocks.   After
       the  write  to medium is performed a verify operation takes place which
       may viewed as a medium read (with appropriate checks) but  without  the
       data  being  returned. Additionally, if BS is set to one, the data read
       back from the medium in the verify operation is compared to the  origi-
       nal data-out buffer.

       The  relationship  between  the  number of logical blocks to be written
       (i.e.  NUM) and the length (in bytes)  of  the  data-out  buffer  (i.e.
       ILEN)  may  be  simply  found  by multiplying the former by the logical
       block size. However if the DEVICE has protection information (PI)  then
       it becomes a bit more complicated. Hence the calculation is left to the
       user with the default ILEN, in the absence of the IF file, being set to
       NUM * 512.

       For  sending large amounts of data to contiguous logical blocks, a sin-
       gle WRITE AND VERIFY command may not be appropriate (e.g. due to  oper-
       ating system limitations). In such cases see the REPEAT section below.

       Arguments to long options are mandatory for short options as well.  The
       options are arranged in alphabetical order based  on  the  long  option

       -S, --16
              Send  a  WRITE  AND VERIFY(16) command. The default is to send a
              WRITE AND VERIFY(10) command unless LBA or NUM are too large for
              the 10 byte variant.

       -b, --bytchk=BC
              where  BC  is  the value to place in the command's BYTCHK field.
              Values between 0 and 3 (inclusive) are accepted. The default  is
              value  is 0 which implies only a write to the medium then a ver-
              ify operation are performed. The only other  value  T10  defines
              currently  is  1  which  does  performs an additional comparison
              between the data-out buffer that was used by the write operation
              and  the  contents  of  the  logical  blocks  read back from the

       -d, --dpo
              Set the DPO (disable page out) bit in the command.  The  default
              is to leave it clear.

       -g, --group=GN
              where  GN  is  the  value to place in the command's GROUP NUMBER
              field.  Values between 0 and 31 (inclusive)  are  accepted.  The
              default is value is 0.

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

       -I, --ilen=ILEN
              where  ILEN  is  the  number of bytes that will be placed in the
              data-out buffer. If the IF file is given then no more than  ILEN
              bytes  are  read from that file. If the IF file does not contain
              ILEN bytes then an error is reported. If the   IF  file  is  not
              given then a data-out buffer with ILEN bytes of 0xff is sent.

       -i, --in=IF
              read  data  (binary) from file named IF. If IF is "-" then stdin
              is used. This data will become the data-out buffer and  will  be
              written  to  the  DEVICE's medium. If BC is 1 then that data-out
              buffer will be held until after the verify  operation  and  com-
              pared to the data read back from the medium.

       -l, --lba=LBA
              where  LBA  is  the  logical block address to start the write to
              medium.  Assumed to be in decimal unless prefixed with  '0x'  or
              has a trailing 'h'.  Must be provided.

       -n, --num=NUM
              where  NUM is the number of blocks, starting at LBA, to write to
              the medium. The default value for NUM is 1.

       -R, --repeat
              this option will continue to do WRITE AND VERIFY commands  until
              the  IF  file  is  exhausted.  This  option  requires  both  the
              --ilen=ILEN and --in=IF options to be given. Each command starts
              at  the  next  logical block address and is for no more than NUM
              blocks. The last command may  be  shorter  with  the  number  of
              blocks  scaled as required. If there are residue bytes a warning
              is sent to stderr. See the REPEAT section.

       -t, --timeout=TO
              where TO is the command timeout value in  seconds.  The  default
              value  is  60  seconds. If NUM is large then command may require
              considerably more time than 60 seconds to complete.

       -v, --verbose
              increase the degree of verbosity (debug messages).

       -V, --version
              output version string then exit.

       -w, --wrprotect=WP
              set the WRPROTECT field in the cdb to WP. The default value is 0
              which  implies no protection information is sent (along with the
              user data) in the data-out buffer.

       For data sizes around a megabyte and larger, it may be  appropriate  to
       send  multiple  SCSI  WRITE AND VERIFY commands due to operating system
       limitations (e.g. pass-through SCSI interfaces often limit  the  amount
       of  data that can be passed with a SCSI command). With this utility the
       mechanism for doing that is the --repeat option.

       In this mode the --ilen=ILEN and --in=IF options  must  be  given.  The
       ILEN and NUM values are treated as a per SCSI command parameters. Up to
       ILEN bytes will be read from  the  IF  file  continually  until  it  is
       exhausted.  If  the IF file is stdin, reading continues until an EOF is
       detected. The data read from each iteration becomes the data-out buffer
       for a new WRITE AND VERIFY command.

       The last read from the file (or stdin) may read less than ILEN bytes in
       which case the number of logical blocks sent to the last WRITE AND VER-
       IFY  is scaled back accordingly. If there is a residual number of bytes
       left after that scaling then that is reported to stderr.

       If an error occurs then that is reported to stderr  and  via  the  exit
       status and the utility stops at that point.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | system/storage/sg3_utils |
       |Stability      | Pass-through uncommitted |
       Other  SCSI  WRITE commands have a Force Unit Access (FUA) bit but that
       is set (implicitly) by WRITE AND VERIFY  commands  hence  there  is  no
       option  to set it. The data-out buffer may still additionally be placed
       in the DEVICE's cache and setting the DPO bit is a hint not to do that.

       Normal SCSI WRITEs can be done with the ddpt and the  sg_dd  utilities.
       The  SCSI WRITE SAME command can be done with the sg_write_same utility
       while the SCSI COMPARE AND WRITE command (sg_compare_and_write utility)
       offers a "test and set" facility.

       Various  numeric  arguments  (e.g. LBA) may include multiplicative suf-
       fixes or be given in hexadecimal. See the "NUMERIC  ARGUMENTS"  section
       in the sg3_utils(8) man page.

       The  exit  status of sg_write_verify is 0 when it is successful. If the
       verify operation fails that is typically indicated with a medium  error
       which leads to an exit status of 3.

       If  BC is set to 1 and the comparison it causes fails this utility will
       indicate the miscompare with an exit status of 14. For other exit  sta-
       tus values see the EXIT STATUS section in the sg3_utils(8) man page.

       To  start  with,  a  simple example: write 1 block of data held in file
       t.bin that is 512 bytes long then write that block  to  LBA  0x1234  on
       /dev/sg4 .

         # sg_write_verify --lba=0x1234 --in=t.bin /dev/sg4

       Since  '--num='  is  not  given then it defaults to 1. Further the ILEN
       value is obtained from the file size of t.bin . To  additionally  do  a
       data-out comparison to the read back data:

         # sg_write_verify -l 0x1234 -i t.bin --bytchk=1 /dev/sg4

       The  ddpt  command  can  do  copies between SCSI devices using READ and
       WRITE commands. However, currently it has no facility to promote  those
       WRITES  to  WRITE AND VERIFY commands. Using a pipe, that could be done
       like this:

         # ddpt if=/dev/sg2 bs=512 bpt=8 count=11 of=- |
       sg_write_verify --in=- -l 0x567 -n 8 --ilen=4096 --repeat /dev/sg4

       Both ddpt and sg_write_verify are configured for segments of 8 512 byte
       logical  blocks.  Since 11 logical blocks are read then first 8 logical
       blocks are copied followed by a copy of the remaining 3  blocks.  Since
       it  is assumed that there is no protection information then the data-in
       and data-out buffers will be 4096 bytes each. For sg_write_verify  this
       needs to be stated explicitly with the --ilen=4096 option.

       Bruno Goncalves and Douglas Gilbert.

       Report bugs to <dgilbert at interlog dot com>.

       Copyright (C) 2014 Douglas Gilbert
       This  software is distributed under a FreeBSD license. There is NO war-
       ranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR  PUR-

       ddpt(in  a  package  of  that name), sg_compare_and_write(8), sg_dd(8),

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source was downloaded from  http://sg.danny.cz/sg/p/sg3_utils-1.42.tgz

       Further information about this software can be found on the open source
       community website at http://sg.danny.cz/sg/sg3_utils.html.

sg3_utils-1.40                     July 2014               WRITE AND VERIFY(8)