Ways to protect data - RAID

Originally 'Redundant Arrays of Inexpensive Disks'. A project at the computer science department of the University of California at Berkeley, under the direction of Professor Katz, in conjunction with Professor John Ousterhout and Professor David Patterson.

The project is reaching its culmination with the implementation of a prototype disk array file server with a capacity of 40 GBytes and a sustained bandwidth of 80 MBytes/second. The server is being interfaced to a 1 Gb/s local area network. A new initiative, which is part of the Sequoia 2000 Project, seeks to construct a geographically distributed storage system spanning disk arrays and automated libraries of optical disks and tapes. The project will extend the interleaved storage techniques so successfully applied to disks to tertiary storage devices. A key element of the research will be to develop techniques for managing latency in the I/O and network paths.

The following standard RAID specifications exist:
RAID 0 Non-redundant striped array
RAID 1 Mirrored arrays
RAID 2 Parallel array with ECC
RAID 3 Parallel array with parity
RAID 4 Striped array with parity
RAID 5 Striped array with rotating parity

The basic idea of RAID (Redundant Array of Independent Disks) is to combine multiple inexpensive disk drives into an array of disk drives to obtain performance, capacity and reliability that exceeds that of a single large drive. The array of drives appears to the host computer as a single logical drive. The Mean Time Between Failure (MTBF) of the array is equal to the MTBF of an individual drive, divided by the number of drives in the array. Because of this, the MTBF of a non-redundant array (RAID 0) is too low for mission-critical systems. However, disk arrays can be made fault-tolerant by redundantly storing information in various ways.