RAID is an acronym for Redundant Array of Independent Disks. The RAID controller card (divide into Hardware and Software) manages the individual physical disks and presents one large logical array to the host computer. The feature of RAID storage system is to provide performance improvements, storage reliability and recovery, and also perform redundant or fault tolerant operations. The RAID is a storage system but not a backup solution.

A basic concept of RAID called EDAP (Extended Data Availability and Protection) which is emphasizing the Redundant and Fault Tolerant Operations. This concept also has been seriously needed by those major businesses such as Mylex, IBM, HP, Compaq, Adaptec, and Infortrend…etc. The RAID controller cards have the ability to continue reading and writing data as the following example lists even if one drive is “off-line”:

1. RAID Auto Error Detection
2. RAID Rebuild and Recovery
3. Hot Spare(RAID Hot Spare)
4. Hot Swap(RAID Hot Swap)
5. Raid Hot Expanding

In a common RAID 5 configuration, Exclusive OR (XOR) is the result of using a Boolean mathematical function. RAID has the Bit Striping and Block Striping two different storage divisions. When the RAID failed, rebuild the Data Blocks in Parity Blocks and Data Stripe calculating by the XOR.

The picture below graphically shows how RAID 5 is put together: