1SG_READCAP(8) SG3_UTILS SG_READCAP(8)
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6 sg_readcap - send SCSI READ CAPACITY command
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9 sg_readcap [--16] [--brief] [--help] [--hex] [--lba=LBA] [--long]
10 [--pmi] [--raw] [--readonly] [--verbose] [--version] [--zbc] DEVICE
11 sg_readcap [-16] [-b] [-h] [-H] [-lba=LBA] [-pmi] [-r] [-R] [-v] [-V]
13 [-z] DEVICE
14
16 The normal action of the SCSI READ CAPACITY command is to fetch the
17 number of blocks (and block size) from the DEVICE.
18 The SCSI READ CAPACITY command (both 10 and 16 byte cdbs) actually
20 yield the block address of the last block and the block size. The num‐
21 ber of blocks is thus one plus the block address of the last block (as
22 blocks are counted origin zero (i.e. starting at block zero)). This is
23 the source of many "off by one" errors.
24 The READ CAPACITY(16) response provides additional information not
26 found in the READ CAPACITY(10) response. This includes protection and
27 logical block provisioning information, plus the number of logical
28 blocks per physical block. So even though the media size may not exceed
29 what READ CAPACITY(10) can show, it may still be useful to examine the
30 response to READ CAPACITY(16). Sadly there are horrible SCSI command
31 set implementations in the wild that crash when the READ CAPACITY(16)
32 command is sent to them.
33 Device capacity is the product of the number of blocks by the block
35 size. This utility outputs this figure in bytes, MiB (1048576 bytes
36 per MiB), GB (1000000000 bytes per GB) and, if large enough, TB (1000
37 GB).
38 If sg_readcap is called without the --long option then the 10 byte cdb
40 version (i.e. READ CAPACITY (10)) is sent to the DEVICE. If the number
41 of blocks in the response is reported as 0xffffffff (i.e. (2**32 - 1) )
42 and the --hex option has not been given, then READ CAPACITY (16) is
43 called and its response is output.
44 This utility supports two command line syntaxes, the preferred one is
46 shown first in the synopsis and explained in this section. A later sec‐
47 tion on the old command line syntax outlines the second group of
48 options.
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51 Arguments to long options are mandatory for short options as well. The
52 options are arranged in alphabetical order based on the long option
53 name.
54 --16 Use the 16 byte cdb variant of the READ CAPACITY command. See
56 the '--long' option. -b, --brief outputs two hex numbers (pre‐
57 fixed with '0x' and space separated) to stdout. The first number
58 is the maximum number of blocks on the device (which is one plus
59 the lba of the last accessible block). The second number is the
60 size in bytes of each block. If the operation fails then "0x0
61 0x0" is written to stdout.
62 -h, --help
64 print out the usage message then exit.
65 -H, --hex
67 output the response to the READ CAPACITY command (either the 10
68 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
69 -L, --lba=LBA
71 used in conjunction with --pmi option. This variant of READ
72 CAPACITY will yield the last block address after LBA prior to a
73 delay. For a disk, given a LBA it yields the highest numbered
74 block on the same cylinder (i.e. before the heads need to move).
75 LBA is assumed to be decimal unless prefixed by "0x" or it has a
76 trailing "h". Defaults to 0. This option was made obsolete in
77 SBC-3 revision 26.
78 -l, --long
80 Use the 16 byte cdb variant of the READ CAPACITY command. The
81 default action is to use the 10 byte cdb variant which limits
82 the maximum block address to (2**32 - 2). When a 10 byte cdb
83 READ CAPACITY command is used on a device whose size is too
84 large then a last block address of 0xffffffff is returned (if
85 the device complies with SBC-2 or later).
86 -O, --old
88 Switch to older style options. Please use as first option.
89 -p, --pmi
91 partial medium indicator: for finding the next block address
92 prior to some delay (e.g. head movement). In the absence of this
93 option, the total number of blocks and the block size of the
94 device are output. Used in conjunction with the --lba=LBA
95 option. This option was made obsolete in SBC-3 revision 26.
96 -r, --raw
98 output response in binary to stdout.
99 -R, --readonly
101 open the DEVICE read-only (e.g. in Unix with the O_RDONLY flag).
102 The default for READ CAPACITY(16) is to open it read-write. The
103 default for READ CAPACITY(10) is to open it read-only so this
104 option does not change anything for this case.
105 -v, --verbose
107 increase level of verbosity. Can be used multiple times.
108 -V, --version
110 outputs version string then exits.
111 -z, --zbc
113 additionally prints out the extra ZBC field (RC_BASIS) in the
114 READ CAPACITY response. Using the option implicitly sets the
115 --16 option.
116
118 The response to READ CAPACITY(16) contains a LBPRZ bit in the SBC-3
119 standard (ANSI INCITS 514-2014). There was also a LBPRZ bit with the
120 same meaning in the Logical block provisioning VPD page (0xb2). Then
121 somewhat confusingly T10 expanded the LBPRZ bit to a 3 bit field in
122 SBC-4 draft revision 7, but only in the LB provisioning VPD page. The
123 reason for the expansion was to report a new "provisioning initializa‐
124 tion pattern" state (when an unmapped logical block is read). The new
125 state has been assigned LBPRZ=2 in the VPD page and it re-uses LBPRZ=0
126 in the READ CAPACITY(16) response. LBPRZ=1 retains the same meaning for
127 both variants, namely that a block of zeroes will be returned when an
128 unmapped logical block is read.
129
131 The exit status of sg_readcap is 0 when it is successful. Otherwise see
132 the sg3_utils(8) man page.
133
135 The options in this section were the only ones available prior to
136 sg3_utils version 1.23 . Since then this utility defaults to the newer
137 command line options which can be overridden by using --old (or -O) as
138 the first option. See the ENVIRONMENT VARIABLES section for another way
139 to force the use of these older command line options.
140 -16 Use the 16 byte cdb variant of the READ CAPACITY command.
142 Equivalent to --long in the main description.
143 -b utility outputs two hex numbers (prefixed with '0x' and space
145 separated) to stdout. The first number is the maximum number of
146 blocks on the device (which is one plus the lba of the last
147 accessible block). The second number is the size of each block.
148 If the operation fails then "0x0 0x0" is written to stdout.
149 Equivalent to --brief in the main description.
150 -h output the usage message then exit. Giving the -? option also
152 outputs the usage message then exits.
153 -H output the response to the READ CAPACITY command (either the 10
155 or 16 byte cdb variant) in ASCII hexadecimal on stdout.
156 -lba=LBA
158 used in conjunction with -pmi option. This variant of READ
159 CAPACITY will yield the last block address after LBA prior to a
160 delay. Equivalent to --lba=LBA in the main description.
161 -N, --new
163 Switch to the newer style options.
164 -pmi partial medium indicator: for finding the next block address
166 prior to some delay (e.g. head movement). In the absence of this
167 switch, the total number of blocks and the block size of the
168 device are output. Equivalent to --pmi in the main description.
169 -r output response in binary (to stdout).
171 -R Equivalent to --readonly in the main description.
173 -v verbose: print out cdb of issued commands prior to execution.
175 '-vv' and '-vvv' are also accepted yielding greater verbosity.
176 -V outputs version string then exits.
178 -R Equivalent to --zbc in the main description.
180
182 Since sg3_utils version 1.23 the environment variable
183 SG3_UTILS_OLD_OPTS can be given. When it is present this utility will
184 expect the older command line options. So the presence of this environ‐
185 ment variable is equivalent to using --old (or -O) as the first command
186 line option.
187
189 Written by Douglas Gilbert
190
192 Copyright © 1999-2020 Douglas Gilbert
193 This software is distributed under the GPL version 2. There is NO war‐
194 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
195 POSE.
196
198 sg_inq(sg3_utils)
199sg3_utils-1.45 January 2020 SG_READCAP(8)