If your dealing with big RAID arrays with a linux 2.6 kernel you will need to tweak your block device readahead settings. This can double or triple your read speeds. The tweak is very easy.
Example of the command is below:
blockdev --setra 16384 /dev/sda
This will only work for RAID arrays. The “–getra” switch will show you your current readahead settings.
Source http://www.pantz.org/software/linux/readaheadtweak.html