Specifications

4–14 Compaq StorageWorks HSG80 Array Controller ACS Version 8.5 Maintenance and Service Guide
Cache Policies Resulting from Cache Module Failures
If the controller detects a full or partial failure of its cache module or ECB, it
automatically reacts to preserve the unwritten data in its cache module. Depending upon
the severity of the failure, the controller chooses an interim caching technique—also
called the cache policy—which it uses until the cache module or ECB is repaired or
replaced.
Table 4–2 shows the cache policies resulting from a full or partial failure of cache module
A in a dual-redundant controller configuration. The consequences shown in this table are
the same for cache module B failures.
Table 4–3 shows the cache policies resulting from a full or partial failure of the ECB
connected to cache module A in a dual-redundant controller configuration. The
consequences shown are the opposite for an ECB failure connected to cache module B.
■ If the ECB is at least 50% charged, the ECB is still good and is charging.
■ If the ECB is less than 50% charged, the ECB is low, but still charging.
Table 4–2 Cache Policies—Cache Module Status
Cache Module Status Cache Policy
Cache A Cache B Unmirrored Cache Mirrored Cache
Good. Good. Data loss: No.
Cache policy: Both controllers support
write-back caching.
Failover: No.
Data loss: No.
Cache policy: Both controllers support
write-back caching.
Failover: No.
Multibit
cache
memory
failure.
Good. Data loss: Forced error and loss of
write-back data for which the multibit
error occurred. Controller A detects and
reports the lost blocks.
Cache policy: Both controllers support
write-back caching.
Failover: No.
Data loss: No. Controller A recovers its lost
write-back data from the mirrored copy on
cache B.
Cache policy: Both controllers support
write-back caching.
Failover: No.