Specifications

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Compaq HSG80 Array Controller ACS Version 8.4 Configuration and CLI Reference Guide
Fault-Tolerance for Write-Back Caching
The cache module supports nonvolatile memory and dynamic cache policies to
protect the availability of its unwritten (write-back) data:
Nonvolatile Memory
The controller can provide write-back caching for any storage unit as long as the
controller’s cache memory is nonvolatile. In other words, to enable write-back
caching, you must provide a backup power source to the cache module to preserve the
unwritten cache data in the event of a power failure. If the cache memory were
volatile—that is, if it didn’t have a backup power supply—the unwritten cache data
would be lost during a power failure.
By default, the controller expects to use an ECB as the backup power source for its
cache module. See “External Cache Battery,” page 1–17, for more information about
the ECB.
However, if your subsystem is backed up by a UPS (uninterruptable power supply),
you can tell the controller to use the UPS as the backup power source with the
CACHE_UPS switch in the command, “SET controller,” page 7–91.
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 you repair or replace the cache
module or ECB.