HP D5970A - NetServer - LCII Configuration Manual page 42

Chapter 4

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. This is the default setting.
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. While this setting
increases performance, it is not recommended unless your system is
equipped with a UPS (uninterruptible power supply).
NOTE
For each logical drive, record the write policy in Worksheet B.

Read Policy
The three Read policies for HP NetRAID are:
Read-Ahead: This is a memory caching feature that tells the controller to
read sequentially ahead of requested data and cache the additional data in
memory, anticipating that the additional data will be requested. Read-
Ahead supplies sequential data faster, but it is not as efficient when
accessing random data.
Normal: This policy does not use the read-ahead memory caching feature.
This policy is efficient when most of the data reads are random.
Adaptive: Adaptive policy causes the read-ahead feature to be used if the
last two disk accesses were in sequential sectors. This is the default
setting.
For each logical drive, record the read policy in Worksheet B.
36
Write Back is not certified for any logical drive used as a
Novell NetWare volume.
Planning