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SG_WRITE_LONG(8)                            SG3_UTILS                            SG_WRITE_LONG(8)

NAME
       sg_write_long - send SCSI WRITE LONG command

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

DESCRIPTION
       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 logical  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  lo-
       cation. After the test the sg_dd utility could be used to write back the original contents
       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 testing.

       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 reassigned (and
       the old location to be added to the grown defect list (PLIST)). This  is  not  easily  re-
       versed  and  uses  (one of the finite number of) the spare sectors set aside for this pur-
       pose. 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.

       In SBC-4 revision 7 all uses of SCSI WRITE LONG (10 and 16 byte) commands were made  obso-
       lete  apart from the case in which the WR_UNCOR bit is set.  The SCSI READ LONG (10 and 16
       byte) commands were made obsolete in the same revision.

OPTIONS
       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 mech-
              anisms such as automatic block reallocation, error recovery  and  various  informa-
              tional 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 overwrite.  Defaults to lba
              0 which is a dangerous block to overwrite 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 op-
              tion,  the default action is to use the provided 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 appropriate xfer_len value may be deduced from  the  error  response
              which is printed (to stderr).

NOTES
       Various  numeric  arguments  (e.g. LBA) may include multiplicative suffixes 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.

EXAMPLES
       This  section  outlines  setting up a block with corrupted data, checking the error condi-
       tion, 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 verbose=4

       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 zeros
       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' op-
       tion 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

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

AUTHORS
       Written by Saeed Bishara. Further work by Douglas Gilbert.

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

COPYRIGHT
       Copyright (C) 2004-2016 Douglas Gilbert
       This  software  is distributed under the GPL version 2. There is NO warranty; not even for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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

sg3_utils-1.42                             January 2016                          SG_WRITE_LONG(8)

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