User Manual

SCSI Commands Reference Manual, Rev. J 231
www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)
3.54 UNMAP command
3.54.1 UNMAP command overview
The UNMAP command (see table 204) requests that the device server cause one or more LBAs to be unmapped. The UNMAP
command is one of the possible commands that shall be implemented by device servers supporting thin provisioning (see
SBC-4).
OPERATION CODE field
The OPERATION CODE field contains the operation code of a command supported by the logical unit and shall be set to the value defined in
table 204.
ANCHOR bit
For a thin provisioned logical unit (see SBC-4):
0 an ANCHOR bit set to zero specifies that any LBA on which an unmap operation is performed shall become deallocated.
1 an ANCHOR bit set to one specifies that any LBA on which an unmap operation is performed shall become anchored.
For a resource provisioned logical unit (see SBC-4), any LBA on which an unmap operation is performed shall become anchored (i.e., the com-
mand is processed as if the ANCHOR bit is set to one). If the ANCHOR bit is set to one, and the ANC_SUP bit in the Logical Block Provisioning
VPD page (see 5.4.13) is set to zero, then the device server shall terminate the command with CHECK CONDITION status with the sense key set
to ILLEGAL REQUEST and the additional sense code set to INVALID FIELD IN CDB.
GROUP NUMBER field
The GROUP NUMBER field specifies the group into which attributes associated with the command should be collected. A GROUP NUMBER field
set to zero specifies that any attributes associated with the command shall not be collected into any group.
PARAMETER LIST LENGTH field
The PARAMETER LIST LENGTH field specifies the length in bytes of the UNMAP parameter data that shall be sent from the application client to
the device server. A PARAMETER LIST LENGTH set to zero specifies that no data shall be sent.
CONTROL byte
The CONTROL byte is described in clause 2.2.7.
Table 204 UNMAP command
Bit
Byte
7 6 5 4 3 2 1 0
0
OPERATION CODE (42h)
1 Reserved ANCHOR
2
Reserved. . .
5
6 Reserved
GROUP NUMBER
7 (MSB)
PARAMETER LIST LENGTH
8 (LSB)
9
CONTROL