Caching Parameters) - IBM DDRS-39130 - Ultrastar 9.1 GB Hard Drive Specifications

7.9.9 Page 8 (Caching Parameters)
7 6
BYTE 0 PS RSVD=0
BYTE 1
BYTE 2
BYTE 3 Read Retention Priority=0
BYTE Disable Pre fetch Transfer Length
4 5
BYTE Minimum Pre fetch
6 7
BYTE Maximum Pre fetch
8 9
BYTE Maximum Pre fetch Ceiling
10 11
BYTE 12 RESERVED = 0
BYTE 13 Number of Cache Segments
Figure 80. Page 8
The caching parameters page defines parameters that affect the use of the cache.
WCE, Write Cache Enable bit, is set to zero to indicate that the drive must issue Good Status for
Write(6) or Write extend(10) command only after successfully writing the data to the media. A WCE bit
of one indicates that the drive may issue Good Status for a Write(6) or Write extend(10) command after
successfully receiving the data but before writing it to the media.
Note: When WCE = 1, a Synchronize Cache command must be done to assume data is written to the
media before powering down the Target.
MF, Multiplication Factor determines how the Maximum Pre-fetch field is interpreted. When this bit is
set the data to pre-fetch is given by the command length multiplied by the value in the Maximum Pre-
fetch field. When this bit is reset the value in the Maximum pre-fetch field is used as the absolute length
to pre-fetch.
RCD, Read Cache Disable bit, of zero indicates that the file may return data requested by a RE AD
command by accessing either the cache or the Read Ahead Buffer, or media. A R C D bit of one indi-
cates that the file shall transfer all data requested by a RE AD command by accessing the media (i.e.,
data cannot be transferred from the cache or Read Ahead Buffer).
Read Retention Priority, Demand Read Retention Priority is not supported.
Write Retention Priority, Write Retention Priority is not supported.
Disable Pre-fetch Transfer Length specifies a number of LBA's which if a read command length exceeds
will cause the drive not to perform read ahead buffering after the command has completed. A value of
zero specifies read ahead is disabled.
BIT
5 4 3 2
Page Code = 08h
Page Length = 0Ch
RESERVED = 0 WCE
Write Retention Priority=0
1 0 Default
88h
0Ch
MF RCD 04h
00h
FFh
FFh
00h
00h
FFh
FFh
FFh
FFh
00h
06h
SCSI C O M M A N D SET
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