Hp Array Controller HSG V8.7 Software Manuale Utente Pagina 66

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212 HSG80 Users Guide
Enabling Mirrored Write-Back Cache
Before configuring dual-redundant controllers and enabling mirroring,
ensure the following conditions are met:
Both array controllers support the same size cache, 64 MB, 128
MB, 256MB, or 512 MB.
Diagnostics indicates that both caches are good.
Both caches have a battery present, if you have not enabled the
CACHE_UPS switch. A battery does not have to be present for
either cache if you enable the CACHE_UPS switch.
No unit errors are outstanding, for example, lost data or data that
cannot be written to devices.
Both array controllers are started and configured in failover mode.
For important considerations when adding or replacing DIMMs in a
mirrored cache configuration, see Replacing DIMMs, page 542.
Selecting a Cache Mode
Before selecting a cache mode you should understand the caching
techniques supported by the cache module.
The cache module supports read, read-ahead, write-through, and write-
back caching techniques that you can enable separately for each storage
unit in a subsystem. For example, you can enable only read and write-
through caching for some units while enabling only write-back caching
for other units.
For details about these caching techniques, seeCaching Techniques,
page 120.
Fault-Tolerance
The cache module supports the following features to protect the
availability of its unwritten (write-back) data:
Nonvolatile memory (required for write-back caching).
Dynamic caching techniques (automatic).
For details about these features, see Fault-Tolerance for Write-Back
Caching, page 121.
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