1SG_READCAP(8) SG3_UTILS SG_READCAP(8)
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6 sg_readcap - sends a SCSI READ CAPACITY command
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9 sg_readcap [--16] [--brief] [--help] [--hex] [--lba=LBA] [--long]
10 [--pmi] [--raw] [--verbose] [--version] DEVICE
11 sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-v] [-V] DEVICE
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15 The normal action of the SCSI READ CAPACITY command is to fetch the
16 number of blocks (and block size) from the DEVICE.
17 The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually
19 yield the block address of the last block and the block size. The num‐
20 ber of blocks is thus one plus the block address of the last block (as
21 blocks are counted origin zero (i.e. starting at block zero)). This is
22 the source of many "off by one" errors.
23 The READ CAPACITY(16) response provides additional information not
25 found in the READ CAPACITY(10) response. This includes protection and
26 thin provisioning information, plus the number of logical blocks per
27 physical block. So even though the media size may not exceed what READ
28 CAPACITY(10) can show, it may still be useful to examine the response
29 to READ CAPACITY(16). Sadly there are horrible SCSI command set imple‐
30 mentations in the wild that crash when the READ CAPACITY(16) command is
31 sent to them.
32 Device capacity is the product of the number of blocks by the block
34 size. This utility outputs this figure in bytes, MiB (1048576 bytes
35 per MiB) and GB (1000000000 bytes per GB).
36 If sg_readcap is called without the --long option then the 10 byte cdb
38 version (i.e. READ CAPACITY (10)) is sent to the DEVICE. If the number
39 of blocks in the response is reported as 0xffffffff (i.e. (2**32 - 1) )
40 and the --hex option has not been given, then READ CAPACITY (16) is
41 called and its response is output.
42 This utility supports two command line syntaxes, the preferred one is
44 shown first in the synopsis and explained in this section. A later sec‐
45 tion on the old command line syntax outlines the second group of
46 options.
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49 Arguments to long options are mandatory for short options as well.
50 -b, --brief
52 outputs two hex numbers (prefixed with '0x' and space separated)
53 to stdout. The first number is the maximum number of blocks on
54 the device (which is one plus the lba of the last accessible
55 block). The second number is the size in bytes of each block. If
56 the operation fails then "0x0 0x0" is written to stdout.
57 -h, --help
59 print out the usage message then exit.
60 -H, --hex
62 output the response to the READ CAPACITY command (either the 10
63 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
64 -L, --lba=LBA
66 used in conjunction with --pmi option. This variant of READ
67 CAPACITY will yield the last block address after LBA prior to a
68 delay. For a disk, given a LBA it yields the highest numbered
69 block on the same cylinder (i.e. before the heads need to move).
70 LBA is assumed to be decimal unless prefixed by "0x" or it has a
71 trailing "h". Defaults to 0.
72 -l, --long
74 Use the 16 byte cdb variant of the READ CAPACITY command. The
75 default action is to use the 10 byte cdb variant which limits
76 the maximum block address to (2**32 - 2). When a 10 byte cdb
77 READ CAPACITY command is used on a device whose size is too
78 large then a last block address of 0xffffffff is returned (if
79 the device complies with SBC-2).
80 --16 Use the 16 byte cdb variant of the READ CAPACITY command. See
82 the '--long' option.
83 -O, --old
85 switch to older style options.
86 -p, --pmi
88 partial medium indicator: for finding the next block address
89 prior to some delay (e.g. head movement). In the absence of this
90 option, the total number of blocks and the block size of the
91 device are output. Used in conjunction with the --lba=LBA
92 option.
93 -r, --raw
95 output response in binary to stdout.
96 -v, --verbose
98 increase level of verbosity. Can be used multiple times.
99 -V, --version
101 outputs version string then exits.
102
104 In the 2.4 series of Linux kernels the DEVICE must be a SCSI generic
105 (sg) device. In the 2.6 series block devices (e.g. SCSI disks and DVD
106 drives) can also be specified. For example "sg_readcap /dev/sda" and
107 "sg_readcap /dev/hdd" (if /dev/hdd is a ATAPI CD/DVD device) will work
108 in the 2.6 series kernels.
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111 The exit status of sg_readcap is 0 when it is successful. Otherwise see
112 the sg3_utils(8) man page.
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115 The options in this section were the only ones available prior to
116 sg3_utils version 1.23 . In sg3_utils version 1.23 and later these
117 older options can be selected by either setting the SG3_UTILS_OLD_OPTS
118 environment variable or using '--old' (or '-O) as the first option.
119 -16 Use the 16 byte cdb variant of the READ CAPACITY command.
121 Equivalent to --long in the main description.
122 -b utility outputs two hex numbers (prefixed with '0x' and space
124 separated) to stdout. The first number is the maximum number of
125 blocks on the device (which is one plus the lba of the last
126 accessible block). The second number is the size of each block.
127 If the operation fails then "0x0 0x0" is written to stdout.
128 Equivalent to --brief in the main description.
129 -h output the usage message then exit. Giving the -? option also
131 outputs the usage message then exits.
132 -H output the response to the READ CAPACITY command (either the 10
134 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
135 -lba=LBA
137 used in conjunction with -pmi option. This variant of READ
138 CAPACITY will yield the last block address after LBA prior to a
139 delay. Equivalent to --lba=LBA in the main description.
140 -N switch to the newer style options.
142 -pmi partial medium indicator: for finding the next block address
144 prior to some delay (e.g. head movement). In the absence of this
145 switch, the total number of blocks and the block size of the
146 device are output. Equivalent to --pmi in the main description.
147 -r output response in binary (to stdout).
149 -v verbose: print out cdb of issued commands prior to execution.
151 '-vv' and '-vvv' are also accepted yielding greater verbosity.
152 -V outputs version string then exits.
154
156 Written by Douglas Gilbert
157
159 Copyright © 1999-2009 Douglas Gilbert
160 This software is distributed under the GPL version 2. There is NO war‐
161 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
162 POSE.
163
165 sg_inq(sg3_utils)
166sg3_utils-1.28 September 2009 SG_READCAP(8)