Digital Equipment HSZ40, Справочное руководство

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SET THIS_CONTROLLER and SET OTHER_CONTROLLER 2–71
HSZ40 Array Controller CLI Reference Manual
CACHE_POLICY=A (Default)
CACHE_POLICY=B
Sets the write-back cache battery policy used by the controller. The policy affects the
availability of RAIDsets and mirrorsets when the write-back cache battery is low:
•
CACHE
_
POLICY
=
A
makes inoperative all RAIDsets and mirrorsets until the battery has
been recharged.
•
CACHE
_
POLICY
=
B
allows write-through access to all RAIDsets and mirrorsets for 10
hours, during which time the battery should be recharging. If the batteries do not
recharge within 10 hours, the RAIDsets and mirrorsets become inoperative.
There is some risk in using
CACHE
_
POLICY
=
B
: since the battery’s state is not good,
there is no guarantee as to how long they will maintain data in the write cache module
should the power fail.
Changing this policy on one controller in a dual-redundant configuration automatically
changes it on the other controller. You must restart a controller for a new
CACHE
_
POLICY
to
take effect.
Regardless of the
CACHE
_
POLICY
, a low or bad battery affects other controller operations as
follows:
•
Stripesets and single-disk unit units with write-back caching enabled are accessed in
write-through (read cache) mode, as long as unwritten cache data has not been lost.
•
RAIDsets and mirrorsets failover to the companion controller’s cache in a dual-
redundant configuration, provided the other cache's batteries are fully charged.
If the batteries are low after controller initialization, unwritten cache data is flushed
from the cache and any RAIDset or mirrorset that does not have access to good
batteries is made inoperative, regardless of the cache policy.
•
If the batteries are bad or missing, RAIDsets and mirrorsets are made inoperative.
•
Write-back caching automatically resumes when the cache batteries are fully
recharged or replaced.