Ubuntu Manpage: sg_write_long - send SCSI WRITE LONG command

Provided by: sg3-utils_1.42-2ubuntu1.18.04.2_amd64

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 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
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
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 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 DEVICE, other than the command (i.e. the cdb). In the absence of
this option, 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
       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 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 © 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.