User Manual

SCSI Commands Reference Manual, Rev. J 232

www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)

3.54.2 UNMAP parameter list

The UNMAP parameter list (see table 205) contains the data sent by an application client along with an UNMAP command.

Included in the data are an UNMAP parameter list header and block descriptors for LBA extents to be processed by the device

server for the UNMAP command. The LBAs specified in the block descriptors may contain overlapping extents, and may be in

any order.

For each specified LBA:

a) a mapped LBA should be unmapped (see SBC-4), or may remain mapped; and

b) an unmapped LBA shall remain unmapped.

UNMAP DATA LENGTH field

The UNMAP DATA LENGTH field specifies the length in bytes of the following data that is available to be transferred from the data-out buffer.

The UNMAP DATA LENGTH does not include the number of bytes in the UNMAP DATA LENGTH field.

UNMAP BLOCK DESCRIPTOR DATA LENGTH field

The UNMAP BLOCK DESCRIPTOR DATA LENGTH field specifies the length in bytes of the UNMAP block descriptor data that is available to be

transferred from the data-out buffer. The UNMAP BLOCK DESCRIPTOR DATA LENGTH should be a multiple of 16. If the UNMAP BLOCK DESCRIP

TOR DATA LENGTH is not a multiple of 16, then the last UNMAP block descriptor is incomplete and shall be ignored. If the UNMAP BLOCK

DESCRIPTOR DATA LENGTH is set to zero, then no UNMAP block descriptors are included in the UNMAP parameter data. This condition shall not

be considered an error.

Table 205 UNMAP parameter list

Bit

Byte

7 6 5 4 3 2 1 0

0 (MSB)

UNMAP DATA LENGTH (n-1)

1 (LSB)

2 (MSB)

UNMAP BLOCK DESCRIPTOR DATA LENGTH (n-7)

3 (LSB)

Reserved. . .

UNMAP block descriptors

UNMAP block descriptor [first] (see table 206). . .

. . .

n-15

UNMAP block descriptor [last] (see table 206). . .