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RAID Last modified: Monday, February 04, 2008
(rād) Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers. RAID allows you to store the same data redundantly (in multiple paces) in a balanced ay to improve overall performance. There are number of different RAID levels: Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost. Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks. Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level. Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used. Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks. Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID. Level 6 -- Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks. Level 0+1 -- A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks. Level 10 -- A Stripe of Mirrors: Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these. Level 7: A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4. RAID S: (also called Parity RAID) EMC Corporation's proprietary striped parity RAID system used in its Symmetrix storage systems. See "Storage Strategies Made Simple" in the "Did You Know...?" section of Webopedia.
EnterpriseNetworkingPlanet EnterpriseNetworkingPlanet provides practical advice and news for running and managing an enterprise network. In-depth articles and news cover topics such as network management, network monitoring, servers, communications, Internet telephony, operating systems, and much more. Open Networks Today Networking news moves at a fast pace, and Open Networks Today lets you keep up with it. Open Networks Today offers its readers the ability to control how news is presented through customizing content filters, discussions, and news feed links. PracticallyNetworked.com PracticallyNetworked.com provides easy-to-understand help for small-network builders. The site contains how-to information for setting up and debugging home-office and small-business networks. Users can also find extensive troubleshooting information, tips on getting applications to work through firewalls, product reviews on network hardware and software, and more. RAID Revs for the Future Now RAID itself is becoming virtualized, abstracting the data from a disk concept into a much broader object-based concept. One concept that is gaining momentum is the idea of linking RAID nodes together into a larger storage mechanism. SmallBusinessComputing.com: Has Your Business Been RAID-ed? RAID, or Redundant Array of Independent (or Inexpensive) Disks, used to be the province of geeks and high-end IT departments. These days, however, it is finding a growing audience among small businesses as a means of increasing the reliability of critical systems, keeping a database online regardless of failures, preventing data loss, and accelerating information access.	Related Categories Data Storage Related Terms data mirroring disk drive disk mirroring disk striping fault tolerance JBOD RAIDb RAIN ROMB server server blade swap