User Manual

SCSI Commands Reference Manual, Rev. J 139
www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)
DPO (Disable Page Out) bit
0 A Disable Page Out (DPO) bit set to zero specifies that the retention priority shall be determined by the RETENTION PRIORITY fields in the
Caching mode page (see 5.3.9).
1 A DPO bit set to one specifies that the device server shall assign the logical blocks accessed by this command the lowest retention prior-
ity for being fetched into or retained by the cache. A DPO bit set to one overrides any retention priority specified in the Caching mode
page. All other aspects of the algorithm implementing the cache replacement strategy are not defined by this manual.
NOTE The DPO bit is used to control replacement of logical blocks in the cache when the application client
has information on the future usage of the logical blocks. If the DPO bit is set to one, the application
client is specifying that the logical blocks accessed by the command are not likely to be accessed
again in the near future and should not be put in the cache nor retained by the cache. If the DPO bit
is set to zero, the application client is specifying that the logical blocks accessed by this command are
likely to be accessed again in the near future.
FUA bit
0 A Force unit Access (FUA) bit set to zero specifies that the device server may read the logical blocks from the volatile cache (if any), the
specified data pattern for that LBA (e.g., the data pattern for unmapped data), the non-volatile cache, or the medium.
1 An FUA bit set to one specifies that the device server shall read the logical blocks from the specified data pattern for that LBA, the
non-volatile cache (if any), or the medium. If a volatile cache contains a more recent version of a logical block, then the device server
shall write that logical block to non-volatile cache or the medium before reading the logical block.
RARC bit
If rebuild assist mode is supported and not enabled, then the rebuild assist recovery control (RARC) bit is ignored. If rebuild assist mode is sup-
ported and enabled, then the RARC bit specifies that read operations are processed as defined in SBC-4.
If the rebuild assist mode is not supported and the RARC bit is set to one, then the device server should 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.
LOGICAL BLOCK ADDRESS field
The LOGICAL BLOCK ADDRESS field specifies the first logical block accessed by this command. If the logical block address exceeds the capacity
of the medium 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 LOGICAL BLOCK ADDRESS OUT OF RANGE.
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.
TRANSFER LENGTH field
The TRANSFER LENGTH field specifies the number of contiguous logical blocks of data that shall be read and transferred to the data-in buffer,
starting with the logical block specified by the LOGICAL BLOCK ADDRESS field. A TRANSFER LENGTH field set to zero specifies that no logical
blocks shall be read. This condition shall not be considered an error. Any other value specifies the number of logical blocks that shall be read. If
the logical block address plus the transfer length exceeds the capacity of the medium, 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 LOGICAL BLOCK ADDRESS OUT OF
RANGE. The TRANSFER LENGTH field is constrained by the MAXIMUM TRANSFER LENGTH field in the Block Limits VPD page.