Quantum 10K II - Manual (Page 141)

SCSI Description
5–74 Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives
MODE SELECT (6) Command (15h) (continued)
Table 5–36 Caching Page — Field Descriptions
Default
Field Value Description
PS 1 Parameters Savable. This bit is only used with the MODE SENSE
command. A returned value of 1 indicates that the target is capable
of saving the page in a non-volatile, vendor-specific location. Bit
reserved with MODE SELECT command.
WCE 1 Write Cache Enable. The default value of 1 enables write-back
caching when processing a WRITE command. The drive returns a
GOOD status and COMMAND COMPLETE only after successfully
wirting all the data to the media.
When WCE = 1, write-back caching is enabled while processing a
WRITE command. The drive returns a GOOD status and COMMAND
COMPLETE only after fetching the data from the initiator and
placing it in the drive’s cache memory.
Note: For maximum data integrity, it is strongly
recommended that when WCE is set to 1, the
Read-Write Error Recovery Page (01h) fields be set
as follows:
• AWRE to 1
• RC to 0
• DCR to 0
• Correction Span set to 170
• Head Offset to 0
• Servo Offset to 0
MF 0 Multiplication Factor (value must be 0). The drive interprets the
minimum and maximum pre-fetch fields values in terms of the
number of logical blocks for each of the respective types of
prefetch.
RCD 0 Read Cache Disable. The default value of 0 enables the read cache
capability and allows the drive to use cache-resident data or
medium data to satisfy a READ command.
When the value is 1, read caching is disabled and the data returned
in response to a READ command is fetched from the medium and
not from the drive’s cache memory.
Demand Read 0 This field advises the drive on the retention priority to assign
Retention Priority data read into the cache that has also been transferred from the
drive to the initiator. Not supported by the drive.
Demand Write 0 This field advises the drive on the retention priority to assign
Retention Priority data written into the cache that has also been transferred from the
cache memory to the medium. Not supported by the drive.
Disable Pre-Fetch FFFFh This field specifies the selective disabling of anticipatory pre-fetch
Transfer Length on long transfer lengths. The value in this field is compared to the
number of sectors requested by the current READ command. If the
number of sectors is greater the than the value specified,
anticipatory pre-fetch is not performed for the command. When 0,
anticipatory pre-fetch is disabled. Ignored by the drive.
(continued)