Ubuntu Manpage: sg_unmap - send SCSI UNMAP command (known as 'trim' in ATA specs)

Provided by: sg3-utils_1.46-3ubuntu2.1_amd64

NAME

       sg_unmap - send SCSI UNMAP command (known as 'trim' in ATA specs)

SYNOPSIS

       sg_unmap   [--all=ST,RN[,LA]]  [--anchor]  [--dry-run]  [--force]  [--grpnum=GN]  [--help]
       [--in=FILE] [--lba=LBA,LBA...] [--num=NUM,NUM...] [--timeout=TO]  [--verbose]  [--version]
       DEVICE

DESCRIPTION

Send a SCSI UNMAP command to DEVICE to unmap one or more logical blocks. This command was
introduced in SBC-3 revision 18 under the broad heading of "logical block provisioning".
Logical blocks may also be unmapped by the SCSI WRITE SAME command; see the sg_write_same
utility. The unmap capability is closely related to the ATA DATA SET MANAGEMENT command
with the "Trim" bit set.

Logical blocks to be unmapped can be specified in one of three ways to this utility. One
way is by supplying the start LBAs to the '--lba=' option and the corresponding number(s)
to unmap to the '--num=' option. Another way is by putting start LBA and number to unmap
pairs in a file whose name is given to the '--in=' option. Alternatively a large segment
or all of a disk (SSD) can be unmapped with the --all=ST_RN[,LA] option. All values are
assumed to be decimal unless prefixed by "0x" (or "0X") or have a trailing "h" (or "H") in
which case they are interpreted as hexadecimal. Suffix multipliers are permitted on
decimal values (e.g. '--num=1m').

When the '--lba=' option is given then the '--num=' option must also be given. If one has
a comma separated list as its argument then the other must have the same number of
elements in its list. The arguments can use a single space as a separator but need to be
in quotes or escaped to not be misinterpreted by the shell.

With the '--in=FILE' option an even number of values must be found and are interpreted as
pairs: the first value in each pair is a starting LBA and the second value is the number
to unmap from that LBA. Everything from and including a "#" on a line is ignored as are
blank lines. Values may be comma, space and tab separated or appear on separate lines.
Each line should not exceed 1023 bytes in length.

Since a lot of data can be lost with this utility, a 15 second "cooling off" period is
given before any UNMAP commands are sent. During this period the user is reminded what
will happen, and to which device, so they can use control-C (or some other technique) to
terminate this utility before any unmapping takes place. This period can be bypassed with
the --force option.

OPTIONS

Arguments to long options are mandatory for short options as well.

-A, --all=ST,RN[,LA]
where ST is the starting LBA, RN is the repeat number which is the maximum number
of blocks in each SCSI UNMAP command, and LA, if given, is the last LBA to unmap.
If LA is not given, then the last LBA on the DEVICE is used. That is obtained by
the SCSI READ CAPACITY command.

-a, --anchor
sets the 'Anchor' bit in the command (introduced in sbc3r22).

-d, --dry-run
perform all the preparation, including opening DEVICE plus sending a 'standard'
SCSI INQUIRY command (and optionally a READ CAPACITY), but exit before performing
any SCSI UNMAP commands.

-f, --force
bypass the 15 second warning period that occurs before any UNMAP commands are sent.

-g, --grpnum=GN
sets the 'Group number' field to GN. Defaults to a value of zero. GN should be a
value between 0 and 63.

-h, --help
output the usage message then exit.

-I, --in=FILE
where FILE is a file name containing pairs of values. The first member of each pair
is a starting LBA and the second member of the pair is the number of logical blocks
to unmap from and including that starting LBA. Values are interpreted as decimal
unless indicated otherwise. This option cannot be present with the '--lba=' option.

-l, --lba=LBA,LBA...
where LBA,LBA... is a string of comma (or space) separated values that are
interpreted as starting logical block addresses. Each number is interpreted as
decimal unless prefixed by '0x' or '0X' (or it has a trailing 'h' or 'H'). An
argument that contains any space separators needs to be quoted (or otherwise
escaped). When this option is given then the '--num=' option must also be given and
they must contain the same number of elements in their arguments.

-n, --num=NUM,NUM...
where NUM,NUM... is a string of comma (or space) separated values that are
interpreted as a number of logical blocks to unmap. Each number is interpreted as
decimal unless prefixed by '0x' or '0X' (or it has a trailing 'h' or 'H'). Note
that 0 blocks is acceptable. An argument that contains any space separators needs
to be quoted (or otherwise escaped). When this option is given then the '--lba='
option must also be given and they must contain the same number of elements in
their arguments.

-t, --timeout=TO
where TO is a timeout value (in seconds) for the UNMAP command. The default value
is 60 seconds.

-v, --verbose
increase the level of verbosity, (i.e. debug output).

-V, --version
print the version string and then exit.

NOTES

Some limits: an LBA can be up to 64 bits, a NUM up to 32 bits (imposed by structure of
UNMAP SCSI command parameter data). The NUM is further constrained by the MAXIMUM UNMAP
LBA COUNT field in the BLOCK LIMITS VPD page (0xb0). The maximum number of LBA,NUM pairs
is limited to 128 by this utility and may be further constrained by the MAXIMUM UNMAP
BLOCK DESCRIPTOR COUNT field in the BLOCK LIMITS VPD page.

Since it is unclear how long the UNMAP command will take to execute a '--timeout=" option
has been provided. The default timeout period is 60 seconds. If all the logical blocks on
a logical unit (e.g. a disk drive) are to be unmapped then the FORMAT UNIT SCSI command
(see the sg_format utility) may be considered as an alternative.

Support for logical block provisioning is indicated by the LBPME bit in the response to
the SCSI READ CAPACITY (16) command (see the sg_readcap utility).

In SBC-3 revision 25 the LBPU and ANC_SUP bits where added to the Logical Block
Provisioning VPD page. When LBPU is set it indicates that the device supports the UNMAP
command. When the ANC_SUP bit is set it indicates the device supports anchored LBAs.

The SCSI UNMAP command does the "right thing" with respect to command queueing. However
its ATA counterpart: the DATA SET MANAGEMENT command with the "Trim" bit set does not
interact well with SATA queueing known as NCQ. To address this problem T13 have
introduced a new command called SFQ DATA SET MANAGEMENT which also has a Trim bit.

EXAMPLES

       In  the  examples  directory of the sg3_utils package there is a sg_unmap_example.txt file
       that shows the format that the '--in=' option accepts.

       To unmap all blocks from and including LBA 0x2000 to the end of the device (e.g.  disk  or
       SSD) with each SCSI UNMAP command given 1024 blocks to unmap:

         sg_unmap --all=0x2000,1k /dev/sg2

       Add  '--force' to bypass the 15 seconds of warnings. So '--force' is appropriate for batch
       files.

EXIT STATUS

       The exit status of sg_unmap is 0 when it is successful. Otherwise see the sg3_utils(8) man
       page.

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2009-2018 Douglas Gilbert
       This  software  is distributed under a FreeBSD license. There is NO warranty; not even for
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.