HP NetRAID Installation and Configuration Guide

Chapter 4 Planning
42
Write Policy
When the IOP writes to disk, the data is first written to the cache on the
assumption that the IOP will read it again soon. The two Write policies are:
• Write-Through: In a write-through cache, data is written to disk at the
same time it is cached. This setting provides better security because
entries are always copied to disk. If no Uninterruptible Power Supply (like
a battery backup unit) is connected, you should use the write-through
setting, because otherwise data could be lost from cache memory in a
power failure.
NOTE Write-Through is the recommended write policy for
HP NetRAID-1Si adapters, because these adapters do not have
battery backup units.
• 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 disk access. Write-Back can be
used if an Uninterruptible Power Supply maintains the data in cache
memory in the event of a power failure.
NOTE Write-Back is NOT recommended unless one of the following
is true:
•
The adapter is HP NetRAID-3Si.
• The system has an uninterruptible power supply (UPS).
Write-Back is not certified for any logical drive used as a
Novell NetWare volume.
For each logical drive, record the write policy in Worksheet B.
!