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A cache-writing strategy in which the array controller receives the data to be
written to disk, stores it in the memory buffer, and immediately sends the
host OS a signal that the write operation is complete, without
waiting until the data is actually written to the disk drive. Within a short time,
the controller, when it is not busy, writes the data to the disk drive.
Write-back caching improves the performance of write operations and the
throughput of the controller card. However, because there is a danger of data loss in
the case of a power failure, storage systems with write-back caching should be
equipped with a UPS or battery backup cache. A UPS provides power long
enough to enable any data in the cache memory to be written to the disk drive. With
battery backup cache, the battery provides power to retain the memory data
for up to 48 hours.
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