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(3) Caching parameters
The following parameters are used to optimize IDD Read-Ahead caching operations under the
system environments. Refer to Chapter 2 of SCSI Logical Interface Specifications for further
details.
a. Read caching parameters
Parameter Default value
• RCD: Disabling Read-Ahead caching operations 0 (enabled)
• WCE: Write Cache Enable 0 (disabled)
• MS: Specifying the multipliers of "minimum
prefetch" and "maximum prefetch"
parameters
0 (Specifying
absolute value)
• DISC: Prefetch operation after track switching
during prefetching
0 (inhibit)
• Number of blocks for which prefetch is suppressed X'FFFF'
• Minimum prefetch X'0000'
• Maximum prefetch X'0XXX'
(Equivalent to
122 KB)
• Number of blocks with maximum prefetch restrictions X'FFFF'
• Number of segments X'4'
Notes:
1. When Read-Ahead caching operations are disabled by the caching parameter, these
parameter settings have no meaning except write cache feature.
2. Determine the parameters in consideration of how the system accesses the disk.
When the access form is not determined uniquely because of the processing method,
the parameters can be re-set actively.
3. For sequential access, the effective access rate can be increased by enabling Read-
Ahead caching operations and Write Cache feature.
(4) Control mode parameters
The following parameters are used to control the tagged queuing and error logging.