sg_unmap man page on DragonFly
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SG_UNMAP(8) SG3_UTILS SG_UNMAP(8)
NAME
sg_unmap - send SCSI UNMAP command (known as 'trim' in ATA specs)
SYNOPSIS
sg_unmap [--anchor] [--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 util‐
ity. The unmap capability is closely related to the ATA DATA SET MAN‐
AGEMENT command with the "Trim" bit set.
Logical blocks to be unmapped can be specified in one of two 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.
The other way is by putting start LBA and number to unmap pairs in a
file whose name is given to the '--in=' 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 mul‐
tipliers 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. Every‐
thing 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.
OPTIONS
Arguments to long options are mandatory for short options as well.
-a, --anchor
sets the 'Anchor' bit in the command (introduced in sbc3r22).
-g, --grpnum=GN
sets the 'Group number' field to GN. Defaults to a value of
zero. GN should be a value between 0 and 31.
-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 val‐
ues 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 con‐
tains 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 ele‐
ments in their arguments.
-n, --num=NUM,NUM...
where NUM,NUM... is a string of comma (or space) separated val‐
ues 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 con‐
tain 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 Logi‐
cal 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 indi‐
cates 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.
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 © 2009-2014 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
sg_format,sg_get_lba_status,sg_readcap,sg_vpd,sg_write_same(sg3_utils)
sg3_utils-1.39 April 2014 SG_UNMAP(8)
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