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SG_READCAP(8)			   SG3_UTILS			 SG_READCAP(8)

NAME
       sg_readcap - sends a SCSI READ CAPACITY command

SYNOPSIS
       sg_readcap  [--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  num‐
       ber  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.

       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).

       This  utility  supports two command line syntaxes, the preferred one is
       shown first in the synopsis and explained in this section. A later sec‐
       tion  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 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.

       -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).

       -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.

       -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
       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.

       The  read  capacity(16) response shows additional information not found
       in the read capacity(10) response. This includes protection information
       and 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).

       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 © 1999-2007 Douglas Gilbert
       This  software is distributed under the GPL version 2. There is NO war‐
       ranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR  PUR‐
       POSE.

SEE ALSO
       sg_inq(sg3_utils)

sg3_utils-1.23			 January 2007			 SG_READCAP(8)
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