sg_write_long - send the SCSI command write long

sg_write_long [--help] [--in=<name>] [--lba=<num>] [--verbose] [--version] [--xfer_len=<num>] <scsi_device>

Send WRITE LONG command to a Linux SCSI device. The buffer to be written to the device is filled with 0xff bytes or read from the given file. This buffer includes the sector data 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. Prior to testing, the sg_dd utility could be used to copy the original contents of the logical block address to some safe location. After testing 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.

--help | -h

output the usage message then exit.

--in=<name> | -i <name>

read data (binary) from given file <name> and use it for the WRITE LONG SCSI command. If <name> is "-" then stdin is read. If this option is not given then a buffer of 0xff bytes is written.

--lba=<num> | -l <num>

the logical block address of the sector to corrupt. 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'. Only 32 bit lbas currently supported.

--verbose | -v

increase the degree of verbosity (debug messages).

--version | -V

output version string then exit.

--xfer_len=<num>|-x <num>

the transfer length in bytes (default to 520). If the given value (or the default) does not match the "long" block size of the device, nothing is written to the device and the appropriate xfer_len value is derived from the error response and printed (to stderr).

The lba and xfer_len numerical arguments may be followed by the following multiplicative suffixes: c C *1; w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB *1,048,576; MB *1,000,000; g G GiB *1,073,741,824; and GB *1,000,000,000 . Also a suffix of the form "x<n>" multiplies the leading number by <n>.

Alternatively numerical values can be given in hexadecimal preceded by either "0x" or "0X". When hex numbers are given multipliers cannot be used.

To read from a defective sector (that, for example, has been filled with 0xff bytes by this utility) use:

sg_dd if=<scsi_device> skip=<lba> of=/dev/null bs=512 count=1

To overwrite to a defective sector use:

sg_dd of=<scsi_device> seek=<lba> if=/dev/zero 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 well formed.

The 10 byte WRITE LONG SCSI command is implemented (not the 16 byte variant). This limits the logical block address to a 32 bit quantity.

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) all set then recovered errors will cause the lba to be reassigned (and the old location to be added to the grown defect list). This is not easily reversed and uses the (finite number) of spare blocks sets 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 sginfo, sg_modes and sg_wr_mode.

Written by Saeed Bishara.

Report bugs to <dgilbert at interlog dot com>.

Copyright © 2004-2005 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.

sg_read_long, sg_dd, sginfo, sg_modes, sg_wr_mode(all in sg3_utils)