User Manual

SCSI Commands Reference Manual, Rev. J 478
www.seagate.com Parameters for direct access devices
MAXIMUM UNMAP LBA COUNT field
The MAXIMUM UNMAP LBA COUNT field set to a non-zero value indicates the maximum number of LBAs that may be unmapped by an UNMAP
command
(see 3.54). If the number of LBAs that may be unmapped by an UNMAP command is constrained only by the amount of data that
may be contained in the UNMAP parameter list (see 3.54.2), then the device server shall set the MAXIMUM UNMAP LBA COUNT field to
FFFF_FFFFh. If the device server implements the UNMAP command, then the value in this field shall be greater than or equal to one. A MAXI-
MUM UNMAP LBA COUNT field set to 0000_0000h indicates that the device server does not implement the UNMAP command.
MAXIMUM UNMAP BLOCK DESCRIPTOR COUNT field
The MAXIMUM UNMAP BLOCK DESCRIPTOR COUNT field set to a non-zero value indicates the maximum number of UNMAP block descriptors
(see 3.54.2) that shall be contained in the parameter data transferred to the device server for an UNMAP command (see 3.54). If there is no limit
on the number of UNMAP block descriptors contained in the parameter data, then the device server shall set the MAXIMUM UNMAP BLOCK
DESCRIPTOR COUNT field to FFFF_FFFFh. If the device server implements the UNMAP command, then the value in the MAXIMUM UNMAP
BLOCK DESCRIPTOR COUNT field shall be greater than or equal to one. A MAXIMUM UNMAP BLOCK DESCRIPTOR COUNT field set to
0000_0000h indicates that the device server does not implement the UNMAP command.
OPTIMAL UNMAP GRANULARITY field
The OPTIMAL UNMAP GRANULARITY field set to a non-zero value indicates the optimal granularity in logical blocks for unmap requests (e.g., an
UNMAP command or a WRITE SAME (16) command with the UNMAP bit set to one). An unmap request with a number of logical blocks that is
not a multiple of this value may result in unmap operations on fewer LBAs than requested. An OPTIMAL UNMAP GRANULARITY field set to
0000_0000h indicates that the device server does not report an optimal unmap granularity.
UGVALID bit
1 An UGVALID (unmap granularity alignment valid) bit set to one indicates that the UNMAP GRANULARITY ALIGNMENT field is valid.
0 A UGAVALID bit set to zero indicates that the UNMAP GRANULARITY ALIGNMENT field is not valid.
UNMAP GRANULARITY ALIGNMENT field
The UNMAP GRANULARITY ALIGNMENT field indicates the LBA of the first logical block to which the OPTIMAL UNMAP GRANULARITY field
applies. The unmap granularity alignment is used to calculate an optimal unmap request starting LBA as follows:
optimal unmap request starting LBA = (n × optimal unmap granularity) + unmap granularity alignment
where:
n is zero or any positive integer value;
optimal unmap granularity is the value in the OPTIMAL UNMAP GRANULARITY field; and
unmap granularity alignment is the value in the UNMAP GRANULARITY ALIGNMENT field.
An unmap request with a starting LBA that is not optimal may result in unmap operations on fewer LBAs than requested.
MAXIMUM WRITE SAME LENGTH field
A MAXIMUM WRITE SAME LENGTH field set to a non-zero value indicates the maximum value that the device server accepts in the NUMBER OF
LOGICAL BLOCKS field for a WRITE SAME command. A MAXIMUM WRITE SAME LENGTH field set to zero indicates that the device server does
not report a limit on the number of logical blocks that may be requested for a single WRITE SAME command.
MAXIMUM ATOMIC TRANSFER LENGTH field
If the ATOMIC BOUNDARY field in the CDB (see 3.68 and 3.69) is set to zero, then a MAXIMUM ATOMIC TRANSFER LENGTH field set to a non-zero
value indicates the maximum atomic transfer length in logical blocks that the device server supports for a single atomic write command (see
3.68 and 3.69) A MAXIMUM ATOMIC TRANSFER LENGTH field set to 0000_0000h indicates that the device server does not indicate a maximum
atomic transfer length. The maximum atomic transfer length indicated by the MAXIMUM ATOMIC TRANSFER LENGTH field shall be less than or
equal to the maximum transfer length indicated by the MAXIMUM TRANSFER LENGTH field. The maximum atomic transfer length indicated by
the MAXIMUM ATOMIC TRANSFER LENGTH field shall be a multiple of the value in the ATOMIC TRANSFER LENGTH GRANULARITY field. If the
ATOMIC BOUNDARY field in the CDB is set to a non-zero value, then the MAXIMUM ATOMIC TRANSFER LENGTH field is ignored.