SCSI_READCAP(8) SG3_UTILS SCSI_READCAP(8)NAME
scsi_readcap - do SCSI READ CAPACITY command on disks
SYNOPSIS
scsi_readcap [--brief] [--help] [--long] [--verbose] DEVICE [DEVICE]*
DESCRIPTION
This Bourne shell script calls the sg_readcap utility on each given DEVICE. This will send a SCSI READ CAPACITY command to each DEVICE.
The default action of this script is to send the 10 byte cdb READ CAPACITY(10) command to each DEVICE. If a response indicates the number
of blocks is greater than or equal to '2**32 - 1' then the READ CAPACITY(16) is sent and its response is output.
OPTIONS
Arguments to long options are mandatory for short options as well.
-b, --brief
shortens the output to two hexadecimal numbers, both prefixed by '0x'. The first number is the number of blocks available and the
second is the size of each blocks in bytes (e.g. '0x12a19eb0 0x200'). If an error is detected '0x0 0x0' is output and the script
continues if there are more DEVICEs.
-h, --help
print out the usage message then exit.
-l, --long
the default is to send the READ CAPACITY(10) command (i.e. the 10 byte cdb variant). When this option is given the READ CAPACITY(16)
command is sent. The latter command yields more information in its response.
-v, --verbose
increase level or verbosity.
EXIT STATUS
The exit status of this script is 0 when it is successful. Otherwise the exit status is that of the last sg_readcap utility called. See the
sg3_utils(8) man page.
AUTHORS
Written by D. Gilbert
COPYRIGHT
Copyright (C) 2009 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR-
POSE.
SEE ALSO
sg_readcap (sg3_utils)
sg3_utils-1.28 October 2009 SCSI_READCAP(8)
Check Out this Related Man Page
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 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.
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
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 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 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).
-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 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.
The read capacity(16) response shows additional information not found in the read capacity(10) response. This includes protection informa-
tion 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 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) 1999-2007 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-1.23 January 2007 SG_READCAP(8)