What is the main goal of RAID technology? Describe the levels 1 through 5.

RAID stands for Redundant Array of Inexpensive (or sometimes "Independent")Disks.

RAID is a method of combining several hard disk drives into one logical unit (two or more disks grouped together to appear as a single device to the host system). RAID technology was developed to address the fault-tolerance and performance limitations of conventional disk storage. It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives. While arrays were once considered complex and relatively specialized storage solutions, today they are easy to use and essential for a broad spectrum of client/server applications.

RAID 1 : Mirrored set without parity. Gives fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs while using a multi-threaded operating system in which supports split seeks, extremely small performance reduction while writing. Array continues to operate so long as at least one drive is functioning. Using RAID 1 along with a separate controller for each disk is sometimes known as duplexing. SNIA definition.

RAID 2: Redundancy through Hamming code. Disks are synchronised and striped inside very little stripes, Frequent in single bytes/words. Hamming codes error correction is computed across corresponding bits on disks, and is stored on multiple parity disks. SNIA definition.

RAID 3: Striped set along with dedicated parity/Bit interleaved parity. This mechanism gives an improved performance and fault tolerance same to RAID 5, but with a dedicated parity disk rather than rotated parity stripes. The single parity disk is a bottle- neck for writing since every write needs updating the parity data. One minor advantages is the dedicated parity disk permits the parity drive to fail and operation will continue without parity or performance penalty.

RAID 4: Block level parity. Identical to RAID 3, but does block-level striping instead of byte-level striping. In this setup, files can be distributed among multiple disks. Each disk operates independently that permits I/O requests to be performed in parallel, by data transfer speeds can suffer because of the type of parity. The error detection is achieved through dedicated parity and is stored in a separate, single disk unit.

RAID 5: It distributes data and parity information across all disks.