RAID
RAID (Redundant Array of Independent Disks) is a group of hard disks that operate together to improve performance or provide fault tolerance and error recovery through data striping, mirroring, and other techniques. RAID uses two or more ordinary hard disks and a RAID disk controller.
From desktops to floor-standing models, RAID come in all sizes. Stand-alone units may include large amounts of cache as well as redundant power supplies. Generally used only with servers, now desktop PCs are also furnished by adding a RAID controller and extra IDE or SCSI disks. New motherboards often have RAID controllers.
RAID Levels
RAID 0 - Speed
Level 0 is disk striping only, which interleaves data across multiple disks for better performance. It does not provide safeguards against failure. RAID 0 is widely used in gaming machines for higher speed.
RAID 1 - Fault Tolerance
Uses disk mirroring, which provides 100% duplication of data. Offers highest reliability, but doubles storage cost. RAID 1 is widely used in business applications.
RAID 2 - Speed
Bits (rather than bytes or groups of bytes) are interleaved across multiple disks. The Connection Machine used this technique, but this is a rare method.
RAID 3 - Speed and Fault Tolerance
Data are striped across three or more drives. Used to achieve the highest data transfer, because all drives operate in parallel. Parity bits are stored on separate, dedicated drives.
RAID 4 - Speed and Fault Tolerance
Similar to Level 3, but manages disks independently rather than in unison. Not often used.
RAID 5 - Speed and Fault Tolerance
Data are striped across three or more drives for performance, and parity bits are used for fault tolerance. The parity bits from two drives are stored on a third drive and are interspersed with user data. RAID 5 is widely used on servers to provide speed and fault tolerance.
RAID 6 - Speed and Fault Tolerance
Similar to RAID 5, but performs two different parity computations or the same computation on overlapping subsets of the data.
RAID 10 - Speed and Fault Tolerance
A combination of RAID 1 and RAID 0 combined. Raid 0 is used for performance, and RAID 1 is used for fault tolerance.
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