SG_READCAP(8)							     SG3_UTILS							     SG_READCAP(8)

NAME

       sg_readcap - sends a 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 num-
       ber 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.

       -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 opera-
	      tion 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 revi-
	      sion 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 max-
	      imum 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).

       --16   Use the 16 byte cdb variant of the READ CAPACITY command. See the '--long' option.

       -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 opera-
	      tion 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 (C) 1999-2011 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A  PARTICULAR  PUR-
       POSE.

SEE ALSO

       sg_inq(sg3_utils)

sg3_utils-1.31							   January 2011 						     SG_READCAP(8)