Digital Equipment HSZ40, Справочное руководство

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2–20 ADD UNIT
___________________________ Note ____________________________
It may take up to 5 minutes for the controller to flush unwritten data from the
cache once you disable write-back caching.
____________________________________________________________
Select
NOWRITEBACK
_
CACHE
for those units for which you want all writes to go directly to
devices without being cached.
Considerations When Using Write-back Caching
The following list summarizes considerations you must be aware of when using
write-back cache.
Two conditions will cause data contained within write-back cache to be lost: if
power from the main power supply and the external cache battery is
interrupted, or if the cache module is removed before the controller flushes
the data from the write-back cache.
•
When restarted, the controller attempts to flush any unflushed data within write-back
cache to the devices. However, by specifying the IGNORE_ERRORS or
IMMEDIATE_SHUTDOWN switch, you allow data to reside in write-back cache
when the controller is turned off, regardless of any errors detected.
•
RAIDsets and mirrorsets require data to be stored in write-back cache to
accomodate the write hole and to increase performance—without regard to the
WRITEBACK_CACHE switch setting.
•
If data is contained within the write-back cache while the subsystem is shut down,
do not perform any hardware changes until after the controller flushes the data to the
devices.
When restarted, the controller attempts to flush any unflushed data within the write-back
cache to the devices. However, by specifying the IGNORE_ERRORS or
IMMEDIATE_SHUTDOWN switch, you allow data to reside in write-back cache when
the controller is turned off, regardless of any errors detected.