man > sg_write_long(8)

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 location. 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 af‐
       ter 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  loca‐
       tion to be added to the grown defect list (PLIST)). This is not easily reversed and uses (one
       of  the  finite  number  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.

       In SBC-4 revision 7 all uses of SCSI WRITE LONG (10 and 16 byte) commands were made  obsolete
       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 mecha‐
              nisms 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 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 transferred to  DE‐
              VICE,  other  than  the command (i.e. the cdb). In the absence of this option, the de‐
              fault 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 de‐
              fault)  does  not match the "long" block size of the device, nothing is written to DE‐
              VICE 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 hexa‐
       decimal. 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  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 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' 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  con‐
       tents:

         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 © 2004-2016 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐
       CHANTABILITY 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)