Specifications

2–14 Controller and Host Concepts
Table 2–3 shows the cache policies resulting from full or partial failure of cache
module A’s ECB in a dual-redundant configuration. Note that when cache module A
is at least 50% charged, the ECB is still operable and charging. When it is less than
50% charged, the ECB is low but still charging. The consequences shown in this table
are opposite for a failure of cache module B’s ECB.
Cache
Board
Failure
Good Same as for DIMM failure. Data integrity: Controller A
recovers all of its write-back data
from the mirrored copy on
cache B.
Cache policy: Both controllers
support write-through caching
only. Controller B cannot execute
mirrored writes because cache
module A cannot mirror
controller B’s unwritten data.
Failover: No
Table 2–2. Cache Policies and Cache Module Status (Continued)
Cache Module Status Cache Policy
Cache A Cache B Unmirrored Cache Mirrored Cache