phpman > man > sg_unmap(8)

SG_UNMAP(8)                                   SG3_UTILS                                  SG_UNMAP(8)



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]  DE‐
       VICE

DESCRIPTION
       Send a SCSI UNMAP command to DEVICE to unmap one or more logical blocks. This command was in‐
       troduced in SBC-3 revision 18 under the broad heading of "logical block provisioning".  Logi‐
       cal  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 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  un‐
       map  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 es‐
       caped 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  op‐
       tion.

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 pre‐
              fixed 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 ac‐
              ceptable. An argument that contains any space separators needs to be quoted (or other‐
              wise  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 logi‐
       cal  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 com‐
       mand 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 MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
       sg_format,sg_get_lba_status,sg_readcap,sg_vpd,sg_write_same(sg3_utils)



sg3_utils-1.43                               March 2018                                  SG_UNMAP(8)