Specifying Storage Subsystem Cache Settings

Use this dialog to specify:

When the cache holds the specified start percentage of unwritten data, a flush is triggered. When the cache flushes down to the specified stop percentage, the flush is stopped. For example, you can specify that the controller start flushing the cache when the cache reaches 80% full and stop flushing the cache when the cache reaches 16% full.

Note: Both the Start flushing and Stop flushing parameters in this version of the storage management software are percentages of the total cache memory. The Stop flushing parameter is NOT equal to the Demand Flush Amount parameter used in previous versions of this storage management software (the Demand Flush Amount parameter was a specified percentage of the Demand Flush Threshold; neither of these parameters are currently used).

How to Change Cache Settings

1 Either (1) select the Storage Subsystem >> Change Cache Settings pull-down menu option; or (2) Use the right mouse button to select the Storage Subsystem in the Logical View, then select Change Cache Settings from the pop-up menu.

Result: The Change Cache Settings dialog is displayed.
2 Select the percentage of unwritten data in the cache that will trigger a cache flush, in the Start Value spinner box.

Note: A percentage that is too low increases the chance that data needed for a host read will not be in the cache. It also increases the number of disk writes necessary to maintain the cache level, increasing system overhead and decreasing performance.
3 Select the percentage of unwritten data held in the cache that will stop a cache flush in progress, in the Stop Value spinner box.

Note: The lower the percentage that you specify, the higher the chance that data for a host read would require a disk read rather than being present in the cache.
4 Select a cache block size that is appropriate for your applications from the Cache block size: drop-down list. Available choices include 4 KB (a good choice for file system or database application use) and 16 KB (a good choice for applications that generate sequential I/O, such as multimedia).
5 Select OK.

Result: The Storage Subsystem controller cache settings are updated.