Redundant Array of Independent Disks (RAID)is a subsystem storage concept that is designed to offer higher levels of protection with regard to data loss that usually occurs from any down time caused by malfunctions compared to the protection offered by conventional disk drives. RAID arrays that are composed of conventional disks are capable to function for hundreds or even thousands of years without losing data because of a disk failure. Additionally, it can also improve the input/output performance, make servicing easier and faster and also let the users to fine-tune the drive system to match the needs of any specific applications. 
You might require RAID for any of the following reasons:
Speed
Increased Storage capacity
Fault tolerance
There are two primary interfaces used for RAID arrays. Traditionally, RAID was done on high-end machines with the use of SCSI interface. Of late, hardware RAID cards for the common and most important IDE/ATA interface have begun to explode in popularity. Therefore, whenever you are designing a system wherein you plan to use RAID, you always have a choice of the interface to make.
There are two types of RAID:
Hardware RAID
Software RAID
Let's take a more detailed look at them.
