Redundant Array of Independent (or Inexpensive) Disks

(raid)

Storage media consisting of two or more disk drives along with software for controlling them in order to produce fault tolerance. The most common use for a RAID system is with servers. There are several RAID levels with the most common being 0, 3, and 5.

• Level 0: Data striping without redundancy. In data striping, data is written into blocks across multiple disks. Level 0 has no fault tolerance but typically improves performance.
• Level 1: Disk mirroring. This provides some fault tolerance.
• Level 2: A parallel array of disks with and error correction data disk.
• Level 3: Same as level 0 with the addition of another disk used for error correction data. With this error correction a disk can be removed from the disk set and replaced and most of the data set can be reconstructed.
• Level 4: A striped array of disks with parity error correction.
• Level 5: Data striping, but at the byte level instead of block level. Error correction is also provided. At this level, a disk can be removed and all data can be reconstructed on the fly.

RAID began as a Computer Science project at the University of California, Berkeley.

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