NAME

       sg_readcap - send SCSI READ CAPACITY command

SYNOPSIS

       sg_readcap   [--16]  [--brief]  [--help]  [--hex]  [--lba=LBA]  [--long]  [--pmi]  [--raw]
       [--verbose] [--version] DEVICE

       sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-v] [-V] DEVICE

DESCRIPTION

       The normal action of the SCSI READ CAPACITY command is to fetch the number of blocks  (and
       block size) from the DEVICE.

       The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually yield the block address
       of the last block and the block size. The number of blocks is  thus  one  plus  the  block
       address  of  the  last  block  (as  blocks are counted origin zero (i.e. starting at block
       zero)). This is the source of many "off by one" errors.

       The READ CAPACITY(16) response provides additional  information  not  found  in  the  READ
       CAPACITY(10)   response.   This   includes   protection  and  logical  block  provisioning
       information, plus the number of logical blocks per physical  block.  So  even  though  the
       media  size  may  not  exceed  what  READ CAPACITY(10) can show, it may still be useful to
       examine the response to READ CAPACITY(16). Sadly  there  are  horrible  SCSI  command  set
       implementations in the wild that crash when the READ CAPACITY(16) command is sent to them.

       Device  capacity  is  the product of the number of blocks by the block size.  This utility
       outputs this figure in bytes, MiB (1048576 bytes per MiB) and  GB  (1000000000  bytes  per
       GB).

       If  sg_readcap is called without the --long option then the 10 byte cdb version (i.e. READ
       CAPACITY (10)) is sent to the DEVICE. If the number of blocks in the response is  reported
       as  0xffffffff  (i.e.  (2**32  -  1)  ) and the --hex option has not been given, then READ
       CAPACITY (16) is called and its response is output.

       This utility supports two command line syntaxes, the preferred one is shown first  in  the
       synopsis  and  explained  in  this section. A later section on the old command line syntax
       outlines the second group of options.

OPTIONS

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

       --16   Use the 16 byte cdb variant of the READ CAPACITY command. See the '--long'  option.
              -b,  --brief  outputs  two  hex numbers (prefixed with '0x' and space separated) to
              stdout. The first number is the maximum number of blocks on the  device  (which  is
              one  plus  the  lba of the last accessible block). The second number is the size in
              bytes of each block. If the operation fails then "0x0 0x0" is written to stdout.

       -h, --help
              print out the usage message then exit.

       -H, --hex
              output the response to the READ CAPACITY command (either the  10  or  16  byte  cdb
              variant) in ASCII hexadecimal on stdout.

       -L, --lba=LBA
              used in conjunction with --pmi option. This variant of READ CAPACITY will yield the
              last block address after LBA prior to a delay. For a disk, given a  LBA  it  yields
              the  highest  numbered  block  on  the same cylinder (i.e. before the heads need to
              move). LBA is assumed to be decimal unless prefixed by "0x" or it  has  a  trailing
              "h". Defaults to 0.  This option was made obsolete in SBC-3 revision 26.

       -l, --long
              Use  the 16 byte cdb variant of the READ CAPACITY command. The default action is to
              use the 10 byte cdb variant which limits the maximum block address to (2**32 -  2).
              When  a  10  byte  cdb  READ CAPACITY command is used on a device whose size is too
              large then a last block address of 0xffffffff is returned (if the  device  complies
              with SBC-2 or later).

       -O, --old
              switch to older style options.

       -p, --pmi
              partial  medium  indicator:  for finding the next block address prior to some delay
              (e.g. head movement). In the absence of this option, the total number of blocks and
              the  block  size  of the device are output.  Used in conjunction with the --lba=LBA
              option. This option was made obsolete in SBC-3 revision 26.

       -r, --raw
              output response in binary to stdout.

       -v, --verbose
              increase level of verbosity. Can be used multiple times.

       -V, --version
              outputs version string then exits.

NOTES

       In the 2.4 series of Linux kernels the DEVICE must be a SCSI generic (sg) device.  In  the
       2.6  series  block  devices  (e.g.  SCSI  disks and DVD drives) can also be specified. For
       example "sg_readcap /dev/sda" and "sg_readcap /dev/hdd" (if /dev/hdd  is  a  ATAPI  CD/DVD
       device) will work in the 2.6 series kernels.

EXIT STATUS

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

OLDER COMMAND LINE OPTIONS

       The options in this section were the only ones available prior to sg3_utils version 1.23 .
       In  sg3_utils version 1.23 and later these older options can be selected by either setting
       the SG3_UTILS_OLD_OPTS environment variable or using '--old' (or '-O) as the first option.

       -16    Use the 16 byte cdb variant of the READ CAPACITY command.  Equivalent to --long  in
              the main description.

       -b     utility outputs two hex numbers (prefixed with '0x' and space separated) to stdout.
              The first number is the maximum number of blocks on the device (which is  one  plus
              the lba of the last accessible block). The second number is the size of each block.
              If the operation fails then "0x0 0x0" is written to stdout.  Equivalent to  --brief
              in the main description.

       -h     output  the  usage  message  then exit. Giving the -? option also outputs the usage
              message then exits.

       -H     output the response to the READ CAPACITY command (either the  10  or  16  byte  cdb
              variant) in ASCII hexadecimal on stdout.

       -lba=LBA
              used  in conjunction with -pmi option. This variant of READ CAPACITY will yield the
              last block address after LBA prior to a delay.  Equivalent to --lba=LBA in the main
              description.

       -N     switch to the newer style options.

       -pmi   partial  medium  indicator:  for finding the next block address prior to some delay
              (e.g. head movement). In the absence of this switch, the total number of blocks and
              the  block  size  of  the  device  are  output.   Equivalent  to  --pmi in the main
              description.

       -r     output response in binary (to stdout).

       -v     verbose: print out cdb of issued commands prior to execution. '-vv' and '-vvv'  are
              also accepted yielding greater verbosity.

       -V     outputs version string then exits.

AUTHORS

       Written by Douglas Gilbert

COPYRIGHT

       Copyright © 1999-2013 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_inq(sg3_utils)