Provided by: sg3-utils_1.33-1_amd64 bug

NAME

       sg_write_same - send the SCSI WRITE SAME command

SYNOPSIS

       sg_write_same [--10] [--16] [--32] [--anchor] [--grpnum=GN] [--help] [--in=IF] [--lba=LBA]
       [--lbdata]  [--num=NUM]  [--pbdata]  [--timeout=TO]  [--unmap]   [--verbose]   [--version]
       [--wrprotect=WPR] [--xferlen=LEN] DEVICE

DESCRIPTION

       Send  the  SCSI  WRITE SAME (10, 16 or 32 byte) command to DEVICE. This command writes the
       given block NUM times to consecutive blocks  on  the  DEVICE  starting  at  logical  block
       address LBA.

       The  length  of  the  block  to  be written multiple times is obtained from either the LEN
       argument, or the length of the given input file IF, or by  calling  READ  CAPACITY(16)  on
       DEVICE.  The  contents  of  the block to be written are obtained from the input file IF or
       zeroes are used. If READ CAPACITY(16) is called (which implies IF was not given)  and  the
       PROT_EN  bit is set then an extra 8 bytes (i.e.  more than the logical block size) of 0xff
       are sent. If READ CAPACITY(16) fails then READ CAPACITY(10) is used to determine the block
       size.

       If  neither  --10,  --16  nor  --32 is given then WRITE SAME(10) is sent unless one of the
       following conditions is met.  If LBA (plus NUM) exceeds 32 bits, NUM exceeds 65535, or the
       --unmap  option is given then WRITE SAME(16) is sent.  The --10, --16 and --32 options are
       mutually exclusive.

       In SBC-3 revision 26 the UNMAP and ANCHOR bits were added to the WRITE SAME (10)  command.
       Since  the  UNMAP bit has been in WRITE SAME (16) and WRITE SAME (32) since SBC-3 revision
       18, the lower of the two (i.e.  WRITE SAME (16)) is the default when the --unmap option is
       given.  To send WRITE SAME (10) use the --10 option.

       Take  care: The WRITE SAME(10, 16 and 32) commands interpret a NUM of zero as write to the
       end of DEVICE. This utility defaults NUM to 1 . The WRITE SAME commands have no IMMED  bit
       so  if  NUM  is large (or zero) then an invocation of this utility could take a long time,
       potentially as long as a FORMAT UNIT command. In such situations the command timeout value
       TO may need to be increased from its default value of 60 seconds. In SBC-3 revision 26 the
       WSNZ (write same no zero) bit was added to the Block Limits VPD page [0xB0].  If  set  the
       WRITE  SAME  commands  will  not  accept  a NUM of zero. The same SBC-3 revision added the
       "Maximum Write Same Length" field to the Block Limits VPD page.

       The Logical Block Provisioning VPD page [0xB2] contains the LBWS and LBW10 bits.  If  LBWS
       is set then WRITE SAME (16) supports the UNMAP bit.  If LBWS10 is set then WRITE SAME (10)
       supports the UNMAP bit. If either LBWS or LBWS10  is  set  and  the  WRITE  SAME  (32)  is
       supported then WRITE SAME (32) supports the UNMAP bit. This is as of SBC-3 revision 26.

       As  a  precaution against an accidental 'sg_write_same /dev/sda' (for example) overwriting
       LBA 0 on /dev/sda with zeroes, at least one of the --in=IF, --lba=LBA or --num=NUM options
       must  be given. Obviously this utility can destroy a lot of user data so check the options
       carefully.

OPTIONS

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

       -R, --10
              send a SCSI WRITE SAME (10) command to DEVICE. The ability to set the --unmap  (and
              --anchor) options to this command was added in SBC-3 revision 26.

       -S, --16
              send a SCSI WRITE SAME (16) command to DEVICE.

       -T, --32
              send a SCSI WRITE SAME (32) command to DEVICE.

       -a, --anchor
              sets  the  ANCHOR  bit  in  the  cdb.  Introduced in SBC-3 revision 22.  That draft
              requires the --unmap option to also be specified.

       -g, --grpnum=GN
              sets the 'Group number' field to GN. Defaults to a value of zero.  GN should  be  a
              value between 0 and 31.

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

       -i, --in=IF
              read  data  (binary)  from  file named IF and use it as the data out buffer for the
              SCSI WRITE SAME command. The length of the data out buffer is --xferlen=LEN or,  if
              that  is  not given, the length of the IF file. If IF is "-" then stdin is read. If
              this option is not given then 0x00 bytes are used as fill with the  length  of  the
              data  out buffer obtained from --xferlen=LEN or by calling READ CAPACITY(16 or 10).
              If the response to READ CAPACITY(16) has the PROT_EN bit set then data  out  buffer
              size is modified accordingly with the last 8 bytes set to 0xff.

       -l, --lba=LBA
              where  LBA  is the logical block address to start the WRITE SAME command.  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'.

       -L, --lbdata
              sets the LBDATA bit in the WRITE SAME cdb.

       -n, --num=NUM
              where  NUM  is  the number of blocks, starting at LBA, to write the data out buffer
              to. The default value for NUM is 1. The value corresponds to the 'Number of logical
              blocks'  field  in the WRITE SAME cdb. Note that a value of 0 in NUM is interpreted
              as write the data out buffer on every block starting at  LBA  to  the  end  of  the
              DEVICE.

       -P, --pbdata
              sets the PBDATA bit in the WRITE SAME cdb.

       -t, --timeout=TO
              where  TO is the command timeout value in seconds. The default value is 60 seconds.
              If NUM is large (or zero) a WRITE SAME command may require considerably  more  time
              than 60 seconds to complete.

       -U, --unmap
              sets the UNMAP bit in the WRITE SAME(10, 16 and 32) cdb. See UNMAP section below.

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

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

       -w, --wrprotect=WPR
              sets  the  "Write protect" field in the WRITE SAME cdb to WPR. The default value is
              zero. WPR should be a value between 0 and 7.  When WPR is 1  or  greater,  and  the
              disk's  protection  type  is  1  or  greater,  then  8  extra  bytes  of protection
              information are expected or generated (to place in the commmand's data out buffer).

       -x, --xferlen=LEN
              where LEN is the data out buffer length. Defaults to the length of the IF file  or,
              if  that is not given, then the READ CAPACITY(16 or 10) command is used to find the
              'Logical block length in bytes'. That figure may be increased by  8  bytes  if  the
              DEVICE's   protection   type   is  1  or  greater  and  the  WRPROTECT  field  (see
              --wrprotect=WPR) is 1 or greater. If both this option and the IF option  are  given
              and  LEN  exceeds  the length of the IF file then LEN is the data out buffer length
              with zeroes used as pad bytes.

UNMAP

       Logical block provisioning is a new term introduced in SBC-3 revision 25 for  the  ability
       to  mark  blocks  as  unused. It is closely related to the ATA DATA SET MANAGEMENT command
       with the "Trim" bit set. For large storage arrays, it is a way to provision less  physical
       storage  than  the READ CAPACITY command reports is available, potentially allocating more
       physical storage when WRITE commands  require  it.  For  flash  memory  it  is  a  way  of
       potentially  saving  power  (and  perhaps access time) when it is known large sections (or
       almost all) of the flash memory is not in use.

       Support for logical block provisioning is indicated by the LBPME bit being set in the READ
       CAPACITY(16)  command response (see the sg_readcap utility).  That implies at least one of
       the UNMAP or WRITE SAME(16) commands is implemented. If the UNMAP command  is  implemented
       then  the  "Maximum  unmap LBA count" and "Maximum unmap block descriptor count" fields in
       the Block Limits VPD page should both be greater than zero. The READ CAPACITY(16)  command
       response  also  contains  a  LBPRZ bit which if set means that if unmapped blocks are read
       then zeroes will be returned for the data (and if protection information is  active,  0xff
       bytes  are  returned  for  that). In SBC-3 revision 27 the same LBPRZ bit was added to the
       Logical Block Provisioning VPD page.

       In SBC-3 revision 25  the  LBPU  and  ANC_SUP  bits  where  added  to  the  Logical  Block
       Provisioning  VPD  page.  When LBPU is set it indicates that the device supports the UNMAP
       command (see the sg_unmap utility). When the ANC_SUP bit is set it  indicates  the  device
       supports anchored LBAs.

       When  the UNMAP bit is set in the cdb then the data out buffer is also sent.  Additionally
       the data section of that data out buffer should be  full  of  0x0  bytes  while  the  data
       protection  block,  8  bytes  at the end if present, should be set to 0xff bytes. If these
       conditions are not met and the LBPRZ bit is set then the UNMAP bit is ignored and the data
       out  buffer  is  written to the DEVICE as if the UNMAP bit was zero. In the absence of the
       --in=IF option, this utility  will  attempt  build  a  data  out  buffer  that  meets  the
       requirements for the UNMAP bit in the cdb to be acted on by the DEVICE.

       Logical  blocks  may  also be unmapped by the SCSI UNMAP and FORMAT UNIT commands (see the
       sg_unmap and sg_format utilities).

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.

EXIT STATUS

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

EXAMPLES

       One simple usage is to write blocks of zero from (and including) a given LBA:

         sg_write_same --lba=0x1234 --num=63 /dev/sdc

       Since --xferlen=LEN has not been given, then this utility  will  call  the  READ  CAPACITY
       command  on  /dev/sdc  to determine the number of bytes in a logical block.  Let us assume
       that is 512 bytes. Since --in=IF is not given a block of zeroes is assumed. So  63  blocks
       of  zeroes  (each  block  containing  512  bytes) will be written from (and including) LBA
       0x1234 . Note that only one block of zeroes is passed to the SCSI WRITE  SAME  command  in
       the data out buffer (as required by SBC-3).

       A  similar  example  follows  but in this case the blocks are "unmapped" ("trimmed" in ATA
       speak) rather than zeroed:

         sg_write_same --unmap -L 0x1234 -n 63 /dev/sdc

       Note that if the LBPRZ bit in the READ CAPACITY(16) response is set  (i.e.   LPPRZ  is  an
       acronym  for  logical  block provisioning read zeroes) then these two examples do the same
       thing, at least seen from the point of view of subsequent reads.

       This utility can also be used to write protection information (PI) on disks formatted with
       a protection type greater than zero. PI is 8 bytes of extra data appended to the user data
       of a logical block: the first two bytes are a CRC (the "guard"), the next  two  bytes  are
       the  "application  tag"  and  the last four bytes are the "reference tag". With protection
       types 1 and 2 if the application tag is 0xffff  then  the  guard  should  not  be  checked
       (against the user data).

       In  this  example we assume the logical block size (of the user data) is 512 bytes and the
       disk has been formatted with protection type 1. Since we are going to modify LBA 2468 then
       we take a copy of it first:

         dd if=/dev/sdb skip=2468 bs=512 of=2468.bin count=1

       The  following command line sets the user data to zeroes and the PI to 8 0xFF bytes on LBA
       2468:

         sg_write_same --lba=2468 /dev/sdb

       Reading back that block should be successful because the application tag is  0xffff  which
       suppresses the guard (CRC) check (which would otherwise be wrong):

         dd if=/dev/sdb skip=2468 bs=512 of=/dev/null count=1

       Now an attempt is made to create a binary file with zeroes in the user data, 0x0000 in the
       application tag and 0xff bytes in the other two PI fields. It is awkward  to  create  0xff
       bytes in a file (in Unix) as the "tr" command below shows:

         dd if=/dev/zero bs=1 count=512 of=ud.bin
         tr "\000" "\377" < /dev/zero | dd bs=1 of=ff_s.bin count=8
         cat ud.bin ff_s.bin > lb.bin
         dd if=/dev/zero bs=1 count=2 seek=514 conv=notrunc of=lb.bin

       The  resulting  file  can be viewed with 'hexdump -C lb.bin' and should contain 520 bytes.
       Now that file can be written to LBA 2468 as follows:

         sg_write_same --lba=2468 wrprotect=3 --in=lb.bin /dev/sdb

       Note the --wrprotect=3 rather than being set to 1, since we want the WRITE SAME command to
       succeed  even though the PI data now indicates the user data is corrupted. When an attempt
       is made to read the LBA, an error should occur:

         dd if=/dev/sdb skip=2468 bs=512 of=/dev/null count=1

       dd errors are not very expressive, if dmesg is checked there should be  a  line  something
       like  this:  "[sdb]   Add.  Sense:  Logical  block  guard  check failed". The block can be
       corrected by doing a "sg_write_same --lba=1234 /dev/sdb" again or restoring  the  original
       contents of that LBA:

         dd if=2468.bin bs=512 seek=2468 of=/dev/sdb conv=notrunc count=1

       Hopefully  the  dd  command would never try to truncate the output file when it is a block
       device.

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2009-2011 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not  even  for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO

       sg_format,sg_get_lba_status,sg_readcap,sg_vpd,sg_unmap(sg3_utils)