phpman > man > sg_write_verify(8)

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



NAME
       sg_write_and_verify - send the SCSI WRITE AND VERIFY command

SYNOPSIS
       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]  DE‐
       VICE

DESCRIPTION
       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 original 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  single  WRITE  AND  VERIFY
       command  may not be appropriate (e.g. due to operating system limitations). In such cases see
       the REPEAT section below.

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

       -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 verify operation are performed. The only other value  T10  defines  cur‐
              rently  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 medium.

       -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 compared 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 de‐
              fault value for NUM is 1.

       -R, --repeat
              this option will continue to do WRITE AND VERIFY commands until the  IF  file  is  ex‐
              hausted.  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 com‐
              plete.

       -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 pro‐
              tection information is sent (along with the user data) in the data-out buffer.

REPEAT
       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  inter‐
       faces often limit the amount of data that can be passed with a SCSI command). With this util‐
       ity 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 con‐
       tinually 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 VERIFY 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.

NOTES
       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 suffixes or be given in hexa‐
       decimal. See the "NUMERIC ARGUMENTS" section in the sg3_utils(8) man page.

EXIT STATUS
       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  miscom‐
       pare  with  an exit status of 14. For other exit status values see the EXIT STATUS section in
       the sg3_utils(8) man page.

EXAMPLES
       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.

AUTHORS
       Bruno Goncalves and Douglas Gilbert.

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

COPYRIGHT
       Copyright © 2014-2018 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not even for MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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



sg3_utils-1.43                                June 2018                          WRITE AND VERIFY(8)