HP StorageWorks HSG80 ACS Solution Software V8.8 for Tru64 UNIX Installation and Configuration Guide (AA-RV1VA-TE, March 2005)

Planning a Subsystem
37HSG80 ACS Solution Software V8.8 for Tru64 UNIX Installation and Configuration Guide
operation is complete. This process is called write-through caching because the
data actually passes through—and is stored in—the cache memory on its way to
the disk drives.
Enabling Mirrored Caching
In mirrored caching, half of each controller’s cache mirrors the companion
controller’s cache, as shown in Figure 11.
The total memory available for cached data is reduced by half, but the level of
protection is greater.
Figure 11: Mirrored caching
Before enabling mirrored caching, make sure the following conditions are met:
■ Both controllers support the same size cache.
■ Diagnostics indicate that both caches are good.
■ No unit errors are outstanding, for example, lost data or data that cannot be
written to devices.
■ Both controllers are started and configured in failover mode.
Cache module A Cache module B
A
cache
Copy of
B
cache
Copy of
A
cache
B
cache
CXO5729A