1SG_UNMAP(8) SG3_UTILS SG_UNMAP(8)
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6 sg_unmap - send SCSI UNMAP command (known as 'trim' in ATA specs)
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9 sg_unmap [--all=ST,RN[,LA]] [--anchor] [--dry-run] [--force] [--grp‐
10 num=GN] [--help] [--in=FILE] [--lba=LBA,LBA...] [--num=NUM,NUM...]
11 [--timeout=TO] [--verbose] [--version] DEVICE
12
14 Send a SCSI UNMAP command to DEVICE to unmap one or more logical
15 blocks. This command was introduced in SBC-3 revision 18 under the
16 broad heading of "logical block provisioning". Logical blocks may also
17 be unmapped by the SCSI WRITE SAME command; see the sg_write_same util‐
18 ity. The unmap capability is closely related to the ATA DATA SET MAN‐
19 AGEMENT command with the "Trim" bit set.
20 Logical blocks to be unmapped can be specified in one of three ways to
22 this utility. One way is by supplying the start LBAs to the '--lba='
23 option and the corresponding number(s) to unmap to the '--num=' option.
24 Another way is by putting start LBA and number to unmap pairs in a file
25 whose name is given to the '--in=' option. Alternatively a large seg‐
26 ment or all of a disk (SSD) can be unmapped with the --all=ST_RN[,LA]
27 option. All values are assumed to be decimal unless prefixed by "0x"
28 (or "0X") or have a trailing "h" (or "H") in which case they are inter‐
29 preted as hexadecimal. Suffix multipliers are permitted on decimal
30 values (e.g. '--num=1m').
31 When the '--lba=' option is given then the '--num=' option must also be
33 given. If one has a comma separated list as its argument then the other
34 must have the same number of elements in its list. The arguments can
35 use a single space as a separator but need to be in quotes or escaped
36 to not be misinterpreted by the shell.
37 With the '--in=FILE' option an even number of values must be found and
39 are interpreted as pairs: the first value in each pair is a starting
40 LBA and the second value is the number to unmap from that LBA. Every‐
41 thing from and including a "#" on a line is ignored as are blank lines.
42 Values may be comma, space and tab separated or appear on separate
43 lines. Each line should not exceed 1023 bytes in length.
44 Since a lot of data can be lost with this utility, a 15 second "cooling
46 off" period is given before any UNMAP commands are sent. During this
47 period the user is reminded what will happen, and to which device, so
48 they can use control-C (or some other technique) to terminate this
49 utility before any unmapping takes place. This period can be bypassed
50 with the --force option.
51
53 Arguments to long options are mandatory for short options as well.
54 -A, --all=ST,RN[,LA]
56 where ST is the starting LBA, RN is the repeat number which is
57 the maximum number of blocks in each SCSI UNMAP command, and LA,
58 if given, is the last LBA to unmap. If LA is not given, then the
59 last LBA on the DEVICE is used. That is obtained by the SCSI
60 READ CAPACITY command.
61 -a, --anchor
63 sets the 'Anchor' bit in the command (introduced in sbc3r22).
64 -d, --dry-run
66 perform all the preparation, including opening DEVICE plus send‐
67 ing a 'standard' SCSI INQUIRY command (and optionally a READ
68 CAPACITY), but exit before performing any SCSI UNMAP commands.
69 -f, --force
71 bypass the 15 second warning period that occurs before any UNMAP
72 commands are sent.
73 -g, --grpnum=GN
75 sets the 'Group number' field to GN. Defaults to a value of
76 zero. GN should be a value between 0 and 63.
77 -h, --help
79 output the usage message then exit.
80 -I, --in=FILE
82 where FILE is a file name containing pairs of values. The first
83 member of each pair is a starting LBA and the second member of
84 the pair is the number of logical blocks to unmap from and
85 including that starting LBA. Values are interpreted as decimal
86 unless indicated otherwise. This option cannot be present with
87 the '--lba=' option.
88 -l, --lba=LBA,LBA...
90 where LBA,LBA... is a string of comma (or space) separated val‐
91 ues that are interpreted as starting logical block addresses.
92 Each number is interpreted as decimal unless prefixed by '0x' or
93 '0X' (or it has a trailing 'h' or 'H'). An argument that con‐
94 tains any space separators needs to be quoted (or otherwise
95 escaped). When this option is given then the '--num=' option
96 must also be given and they must contain the same number of ele‐
97 ments in their arguments.
98 -n, --num=NUM,NUM...
100 where NUM,NUM... is a string of comma (or space) separated val‐
101 ues that are interpreted as a number of logical blocks to unmap.
102 Each number is interpreted as decimal unless prefixed by '0x' or
103 '0X' (or it has a trailing 'h' or 'H'). Note that 0 blocks is
104 acceptable. An argument that contains any space separators needs
105 to be quoted (or otherwise escaped). When this option is given
106 then the '--lba=' option must also be given and they must con‐
107 tain the same number of elements in their arguments.
108 -t, --timeout=TO
110 where TO is a timeout value (in seconds) for the UNMAP command.
111 The default value is 60 seconds.
112 -v, --verbose
114 increase the level of verbosity, (i.e. debug output).
115 -V, --version
117 print the version string and then exit.
118
120 Some limits: an LBA can be up to 64 bits, a NUM up to 32 bits (imposed
121 by structure of UNMAP SCSI command parameter data). The NUM is further
122 constrained by the MAXIMUM UNMAP LBA COUNT field in the BLOCK LIMITS
123 VPD page (0xb0). The maximum number of LBA,NUM pairs is limited to 128
124 by this utility and may be further constrained by the MAXIMUM UNMAP
125 BLOCK DESCRIPTOR COUNT field in the BLOCK LIMITS VPD page.
126 Since it is unclear how long the UNMAP command will take to execute a
128 '--timeout=" option has been provided. The default timeout period is 60
129 seconds. If all the logical blocks on a logical unit (e.g. a disk
130 drive) are to be unmapped then the FORMAT UNIT SCSI command (see the
131 sg_format utility) may be considered as an alternative.
132 Support for logical block provisioning is indicated by the LBPME bit in
134 the response to the SCSI READ CAPACITY (16) command (see the sg_readcap
135 utility).
136 In SBC-3 revision 25 the LBPU and ANC_SUP bits where added to the Logi‐
138 cal Block Provisioning VPD page. When LBPU is set it indicates that the
139 device supports the UNMAP command. When the ANC_SUP bit is set it indi‐
140 cates the device supports anchored LBAs.
141 The SCSI UNMAP command does the "right thing" with respect to command
143 queueing. However its ATA counterpart: the DATA SET MANAGEMENT command
144 with the "Trim" bit set does not interact well with SATA queueing known
145 as NCQ. To address this problem T13 have introduced a new command
146 called SFQ DATA SET MANAGEMENT which also has a Trim bit.
147
149 In the examples directory of the sg3_utils package there is a
150 sg_unmap_example.txt file that shows the format that the '--in=' option
151 accepts.
152 To unmap all blocks from and including LBA 0x2000 to the end of the
154 device (e.g. disk or SSD) with each SCSI UNMAP command given 1024
155 blocks to unmap:
156 sg_unmap --all=0x2000,1k /dev/sg2
158 Add '--force' to bypass the 15 seconds of warnings. So '--force' is
160 appropriate for batch files.
161
163 The exit status of sg_unmap is 0 when it is successful. Otherwise see
164 the sg3_utils(8) man page.
165
167 Written by Douglas Gilbert.
168
170 Report bugs to <dgilbert at interlog dot com>.
171
173 Copyright © 2009-2018 Douglas Gilbert
174 This software is distributed under a FreeBSD license. There is NO war‐
175 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
176 POSE.
177
179 sg_format,sg_get_lba_status,sg_readcap,sg_vpd,sg_write_same(sg3_utils)
180sg3_utils-1.43 March 2018 SG_UNMAP(8)