HP P3410A HP NetRAID 1M/2M Installation & Configuration - Page 177

Write Policy, Write Back, Write Through

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Glossary Write Policy: When the processor writes to main memory, the data is first written to the cache on the assumption that the processor will probably read it again soon. The two Write policies for HP NetRAID are: • Write Back: In a write-back cache, data is written to main memory only when it is forced out of the cache. Write-back requires the cache to initiate a main memory write of the flushed entry, followed (for a processor read) by a main memory read. Write-back is efficient, because an entry may be written many times in the cache without a main memory access. • Write Through: In a write-through cache, data is written to main memory at the same time as it is cached. Write-through is simpler than write-back, because an entry that is to be replaced can be overwritten in the cache, as it will already have been copied to main memory. WriteThrough is the recommended write policy for HP NetRAID-1M adapter, because this adapter does not have a battery backup unit. 169

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Glossary
169
Write Policy:
When the processor writes to main memory, the data is first
written to the cache on the assumption that the processor will probably read it
again soon. The two Write policies for HP NetRAID are:
•
Write Back
: In a write-back cache, data is written to main memory only
when it is forced out of the cache. Write-back requires the cache to initiate
a main memory write of the flushed entry, followed (for a processor read)
by a main memory read. Write-back is efficient, because an entry may be
written many times in the cache without a main memory access.
•
Write Through
: In a write-through cache, data is written to main
memory at the same time as it is cached. Write-through is simpler than
write-back, because an entry that is to be replaced can be overwritten in
the cache, as it will already have been copied to main memory. Write-
Through is the recommended write policy for HP NetRAID-1M adapter,
because this adapter does not have a battery backup unit.