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man pages section 1M: System Administration Commands

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Updated: July 2017

sg_write_long (1m)


sg_write_long - send the SCSI WRITE LONG command


sg_write_long   [--16]   [--cor_dis]   [--help]  [--in=IF]  [--lba=LBA]
[--pblock] [--verbose] [--version] [--wr_uncor] [--xfer_len=BTL] DEVICE


SG_WRITE_LONG(8)                   SG3_UTILS                  SG_WRITE_LONG(8)

       sg_write_long - send the SCSI WRITE LONG command

       sg_write_long   [--16]   [--cor_dis]   [--help]  [--in=IF]  [--lba=LBA]
       [--pblock] [--verbose] [--version] [--wr_uncor] [--xfer_len=BTL] DEVICE

       Send the SCSI WRITE LONG (10 or 16 byte) command to DEVICE. The  buffer
       to  be written to the DEVICE is filled with 0xff bytes or read from the
       IF file. This buffer includes the logical data (e.g. 512 bytes) and the
       ECC bytes.

       This utility can be used to generate a MEDIUM ERROR at a specific logi-
       cal block address. This can be useful for testing error handling. Prior
       to  such  a  test, the sg_dd utility could be used to copy the original
       contents of the logical block address to some safe location. After  the
       test  the  sg_dd  utility could be used to write back the original con-
       tents of the logical block address. An alternate strategy would  be  to
       read the "long" contents of the logical block address with sg_read_long
       utility prior to testing and restore it with this utility  after  test-

       Take care: If recoverable errors are being injected (e.g. only one or a
       few bits changed so that the ECC is able to correct the data) then care
       should  be  taken  with the settings in the "read write error recovery"
       mode page.  Specifically if the  ARRE  (for  reads)  and/or  AWRE  (for
       writes)  are  set  then recovered errors will cause the lba to be reas-
       signed (and the old location to be  added  to  the  grown  defect  list
       (PLIST)).  This is not easily reversed and uses (one of the finite num-
       ber of) the spare sectors set aside for this purpose. If in doubt it is
       probably  safest  to  clear  the  ARRE and AWRE bits. These bits can be
       checked and modified with the sdparm utility.  For example: "sdparm  -c
       AWRE,ARRE /dev/sda" will clear the bits until the disk is power cycled.

       Arguments to long options are mandatory for short options as well.

       -S, --16
              send  a  SCSI  WRITE  LONG  (16)  command to DEVICE. The default
              action (in the absence of this option) is to send a  SCSI  WRITE
              LONG (10) command.

       -c, --cor_dis
              sets  the correction disabled (i.e 'COR_DIS') bit. This inhibits
              various other mechanisms such as automatic  block  reallocation,
              error  recovery  and  various informational exception conditions
              being triggered.  This bit is relatively new in SBC-3 .

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

       -i, --in=IF
              read data (binary) from file named IF and use it  for  the  SCSI
              WRITE  LONG  command.  If  IF is "-" then stdin is read. If this
              option is not given then 0xff bytes are used as fill.

       -l, --lba=LBA
              where LBA is the logical block address of the  sector  to  over-
              write.   Defaults  to  lba 0 which is a dangerous block to over-
              write on a disk that is in use. Assumed to be in decimal  unless
              prefixed  with '0x' or has a trailing 'h'. If LBA is larger than
              can fit in 32 bits then the --16 option should be used.

       -p, --pblock
              sets the physical  block  (i.e  'PBLOCK')  bit.  This  instructs
              DEVICE  to  use the given data (unless --wr_uncor is also given)
              to write to the physical block specified  by  LBA.  The  default
              action  is  to  write  to the logical block corresponding to the
              given lba.  This bit is relatively new in SBC-3 .

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

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

       -w, --wr_uncor
              sets  the  "write  uncorrected"  (i.e  'WR_UNCOR')   bit.   This
              instructs  the  DEVICE  to  flag  the given lba (or the physical
              block that contains it if --pblock is also given) as  having  an
              unrecoverable  error associated with it. Note: no data is trans-
              ferred to DEVICE, other than the command (i.e. the cdb). In  the
              absence  of  this  option, the default action is to use the pro-
              vided data or 0xff bytes (--xfer_len=BTL in length) and write it
              to DEVICE.  This bit is relatively new in SBC-3 .

       -x, --xfer_len=BTL
              where  BTL  is the byte transfer length (default to 520). If the
              given value (or the default) does not  match  the  "long"  block
              size  of the device, nothing is written to DEVICE and the appro-
              priate xfer_len value may be deduced  from  the  error  response
              which is printed (to stderr).

       See attributes(5) for descriptions of the following attributes:

       |Availability   | system/storage/sg3_utils |
       |Stability      | Uncommitted              |
       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 10 byte SCSI WRITE LONG command limits the logical block address to
       a 32 bit quantity. For larger LBAs use the --16  option  for  the  SCSI
       WRITE LONG (16) command.

       This  section outlines setting up a block with corrupted data, checking
       the error condition, then restoring useful contents to that sector.

       First, if the  data  in  a  sector  is  important,  save  it  with  the
       sg_read_long utility:

         sg_read_long --lba=0x1234 --out=0x1234_1.img -x BTL /dev/sda

       This utility may need to be executed several time in order to determine
       what the correct value for BTL is.  Next use this utility to  "corrupt"
       that sector. That might be done with:

         sg_write_long --lba=0x1234 -x BTL /dev/sda

       This  will  write a sector (and ECC data) of 0xff bytes. Some disks may
       reject this (at least one of the author's does). Another approach is to
       copy the 0x1234_1.img file (to 0x1234_2.img in this example) and change
       some values with a hex editor. Then write the changed image with:

         sg_write_long --lba=0x1234 --in=0x1234_2.img -x BTL /dev/sda

       Yet another approach is to use the --wr_uncor option, if supported:

         sg_write_long --lba=0x1234 --wr_uncor /dev/sda

       Next we use the sg_dd utility to check that the  sector  is  corrupted.
       Here is an example:

         sg_dd  if=/dev/sda  blk_sgio=1  skip=0x1234  of=. bs=512 count=1 ver-

       Notice that the "blk_sgio=1" option is given. This is to make sure that
       the  sector  is  read  (and no others) and the error is fully reported.
       The "blk_sgio=1" option causes the SG_IO ioctl  to  be  used  by  sg_dd
       rather than the block subsystem.

       Finally  we  should  restore  sector 0x1234 to a non-corrupted state. A
       sector full of zeroes could be written with:

         sg_dd if=/dev/zero of=/dev/sda blk_sgio=1 seek=0x1234 bs=512 count=1

       This will result in a sector (block) with 512 bytes of  0x0  without  a
       MEDIUM  ERROR since the ECC and associated data will be regenerated and
       thus well formed. The 'blk_sgio=1' option is  even  more  important  in
       this  case as it may stop the block subsystem doing a read before write
       (since the read will most likely fail).  Another approach is  to  write
       back the original contents:

         sg_write_long --lba=0x1234 --in=0x1234_1.img -x BTL /dev/sda

       The  exit status of sg_write_long is 0 when it is successful. Otherwise
       see the sg3_utils(8) man page.

       Written by Saeed Bishara. Further work by Douglas Gilbert.

       Report bugs to <dgilbert at interlog dot com>.

       Copyright (C) 2004-2009 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO  war-
       ranty;  not  even  for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR-

       sg_read_long, sg_dd (both in sg3_utils), sdparm(sdparm)

       This    software    was    built    from    source     available     at
       https://java.net/projects/solaris-userland.    The  original  community
       source was downloaded from  http://sg.danny.cz/sg/p/sg3_utils-1.33.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-1.27                    March 2009                  SG_WRITE_LONG(8)