Dell Shared PowerEdge RAID Controller (PERC) 8 For Dell PowerEdge VRTX Systems User’s Guide

The read policy of a virtual disk determines how the controller handles reads to that virtual disk. The read policies are:

• Read Ahead — Allows the controller to read sequentially ahead of the requested data and store the additional data in cache memory. This speeds up reads for sequential data, but there is little improvement when accessing random data.
• No Read Ahead — Disables the Read-Ahead capability.
• Adaptive Read Ahead — Read Ahead Mode is used when the two most recent disk accesses occurred in sequential sectors, otherwise the controller reverts to No Read Ahead mode.