Although seven levels of RAID are commonly defined, almost unlimited variations can be created by combining different elements from each. For the purpose of this discussion, we will focus on the defined levels in order to understand how raid data recovery works.
RAID 0 doesn't really produce any redundancy (if one drive fails, the data on the RAID is lost), although it is useful for performance purposes. It uses the technique called striping to spread data blocks across multiple drives. Because data is striped across different drives, the computer can access the data twice as fast in a two drive configuration. RAID 0 provides for twice as much data to be written in the same amount of time. RAID 0 achieves this performance increase without reducing the combined amount of storage space. The lack of RAID data recovery makes RAID 0 unappealing to those looking for the ability to survive a hard drive failure.
RAID 1 works without striping, so it doesn't have the same performance increases as found with RAID 0. Using a technique called mirroring, RAID 1 maintains an identical copy of the main (or "active") drive at all times on the "mirror" drive. If the active drive fails, it can be removed and the mirror drive can be set to operate in its place. Disadvantages of RAID 1 include the loss of hard drive space (the storage capacity is that of the smallest drive), the lack of performance improvements, and the time it takes to change from the active to the mirrored drive in the event of failure.
RAID 2 requires at least three drives. Synchronization of disk rotations is achieved and a stripe is created so that every subsequent bit is placed on a different disk. One disk is used to store parity information that can be used to correct errors. If one drive fails, the disk array continues to operate. Because the system writes data across multiple disks, performance gains are realized and the use of a parity drive enhances survivability.