Compaq HSZ80 manual Readcache Default, Noreadcache, Readaheadcache Default, Noreadaheadcache

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Select PREFERRED_PATH=THIS_CONTROLLER to instruct “this controller” to bring the units online.

Select PREFERRED_PATH=OTHER_CONTROLLER to instruct the “other controller” to bring the units online.

See Chapter 2 for information regarding multiple bus failover.

IMPORTANT: Subsystem performance is better if target ID numbers are bal- anced across the dual-redundant pair.

READ_CACHE (Default)

NOREAD_CACHE

Sets the controller’s read-cache policy function.

Read caching improves performance in almost all situations. Therefore, it is recommended you leave its default setting, READ_CACHE, enabled. However, under certain conditions, such as when performing a backup, read caching may not be necessary since only a small amount of data is cached. In such instances, it may be beneficial to disable the read cache function and remove the processing overhead associated with caching data.

READAHEAD_CACHE (Default)

NOREADAHEAD_CACHE

Enables the controller to keep track of read I/Os. If the controller detects sequential read I/Os from the host, it will then try to keep ahead of the host by reading the next sequential blocks of data (those the host has not yet requested) and put the data in cache. This process is sometimes referred to as prefetch. The controller can detect multiple sequential I/O requests across multiple units.

Read ahead caching improves host application performance since the data will be read from the controller cache instead of disk. Read ahead caching is the default for units.

If you are adding a unit that is not expected to get sequential I/O requests, select NOREADAHEAD_CACHE for the unit.

Compaq HSZ80 Array Controller ACS Version 8.3 Configuration and CLI Reference Guide