HP P3410A HP NetRAID 1M/2M Installation & Configuration - Page 46

Chapter 4 Planning Read Policy ! The three Read policies for HP NetRAID are: • Read-Ahead: This is a memory caching feature that tells the adapter 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. For each logical drive, record the read policy in Worksheet B. Cache Policy ! HP NetRAID lets you choose one of two cache policies: • Cached I/O: Reads are always cached regardless of randomness. The selected Read policy (Read-Ahead, Normal, or Adaptive) and Write policy (Write-Through and Write-Back) always applies. • Direct I/O: First reads to a new location always come directly from the disk. If a location is read repeatedly, then the Read policy as selected will apply and the read data will be cached. Read data is cached only if accessed repeatedly. With 100% randomness, nothing is cached. For each logical drive, record the cache policy in Worksheet B. 38