Originally Posted by WiredTree Zac

RAID-1 is good for general webhosting. It only prevents against disk failure as any changed made on the RAID is made to both disks at once, so you still need a backup plan.

We use RAID-5 and RAID-10 on more specialized applications like fileservers or database servers. VPS server performance also greatly improves from using RAID-10 since disk I/O is oftentimes a bottleneck.

http://www.acnc.com/04_00.html is a good site for describing raid levels.