Apple Xsan 2 (Third Edition) - Manual (Page 36)

Enable Read Prefetching
Read prefetching is a technique that improves file system read performance when
data is being read sequentially, as in the case of audio or video streaming, for example.
When read prefetching is enabled, the RAID controller assumes that a read request for
a block of data will be followed by requests for adjacent data blocks. To prepare for
these requests, the RAID controller reads the requested data and the following data,
and stores it in cache memory. Then, if the data is requested, it’s retrieved from the fast
cache instead of from the slower disk drives.
36 Chapter 2 Planning a Storage Area Network