HP P3410A HP NetRAID Series User Guide - Page 156

Write Policy, Write-Through, Write-Back

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Glossary Write Policy: When the processor writes to disk, 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-Through: In a write-through cache, data is written to disk 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 disk. • Write-Back: In a write-back cache, data is written to disk only when it is forced out of the cache. Write-back is efficient, because an entry may be written many times in the cache without a main memory access. NOTE Write-Back is NOT recommended unless one of the following is true: • The HP NetRAID adapter is an HP NetRAID-3Si, which has a Battery Backup Unit. • Your system is equipped with a UPS (uninterruptible power supply). • Your system is an HP NetServer LH 3000/3000r, LH 6000/6000r, or LT 6000r that is equipped with a charged accessory Battery Backup Module. Write-Back is not certified for any logical drive used as a Novell NetWare volume. 150

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Glossary
150
Write Policy:
When the processor writes to disk, 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-Through
: In a write-through cache, data is written to disk 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 disk.
•
Write-Back
: In a write-back cache, data is written to disk only when it is
forced out of the cache. Write-back is efficient, because an entry may be
written many times in the cache without a main memory access.
NOTE
Write-Back is NOT recommended unless one of the following
is true:
•
The HP NetRAID adapter is an HP NetRAID-3Si, which
has a Battery Backup Unit.
•
Your system is equipped with a UPS (uninterruptible
power supply).
•
Your system is an HP NetServer LH 3000/3000r,
LH 6000/6000r, or LT 6000r that is equipped with a
charged accessory Battery Backup Module.
Write-Back is not certified for any logical drive used as a
Novell NetWare volume.