Hard Disk Drive RAID is basically an acronym for Redundant Array of Indepedent Disks. It combines many hard disk drives into one single logical drive. The four most popular one's which you will most likely want to have setup on your server will be covered below.
RAID 0: Striped Set - A RAID 0 setup splits data evenly across two or more disks. It is important to note that RAID 0 was not one of the original RAID levels, and is not redundant. If one drive goes down your server will need to be restored from backup.
RAID 1: Mirrored Set - A Raid 1 setup creates an exact copy (or mirror) of data on two or more disks. A typical setup just has two drives that are setup to mirror data. If one drive goes down your server will still be functional until a scheduled drive replacement can be installed.
RAID 5: Striped Set with Parity - A RAID 5 setup uses block-level striping with parity data distributed across all disks in the RAID Array. This means you can have one drive fail and your server will remain functional until a scheduled drive replacement can be installed. RAID 5 also increases read/write speeds while using the available disk space efficiently.
RAID 10: Stripe of mirrors - A RAID 10 setup, sometimes called RAID 1+0 or RAID 1&0, consists of two or more mirrored (RAID 1) arrays striped (Raid 0) for redundancy and performance. This means that you can have one drive from each of the mirrored arrays fail and still maintain server uptime and data integrity until downtime can be scheduled to replace the failed drive(s). RAID 10 requires a minimum of 4 hard drives to implement; having 2 drives in each mirrored set. RAID 10 the primary choice for high-load databases servers because of the faster write speeds due to lack of parity data.