RAID Array 450 HSZ50 HSOF Software Version 5.7 for Compaq Tru64 UNIX Release Notes

RAID Array 450 HSZ50 HSOF Software Version 5.7 for Compaq Tru64 UNIX
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5.2 Write-Back Cache Batteries and Battery Handling
Diagnostic testing is performed on the write-back cache batteries when the
controller first initializes, and then periodically after the batteries have become
fully charged. The following paragraphs clarify battery-related topics.
5.2.1 CACHE_UPS Switch Use
If the SET controller CACHE_UPS switch is activated, the only action taken
in the event of battery failure is to send an error message.
The CACHE_UPS is not intended to replace batteries. The switch is intended
to control the impact that the current battery state has on cache policy. Battery
state is still reported and if the power fails and UPS is broken or exhausted the
batteries will still maintain cache contents.
When the CACHE_UPS switch is enabled, an uninterruptible power supply
(UPS) is assumed to be in use to maintain power to the write-back cache
module in the event of a power failure. Note that the HSOF software does not
have the capability to monitor the remaining capacity of an external UPS.
There are many variables in a UPS configuration; some configurations might
put data at risk if the UPS is exhausted. If UPS power is lost to the host/storage
system without warning, write-back cache data is maintained by the cache
batteries only. With CACHE_UPS set, if UPS power is last and if the cache
batteries have failed, data could be at risk.
CAUTION
Use of this setting without a functional UPS in place could result in
data loss if power is interrupted and batteries have failed.