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Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives.
Diagram of a RAID 1 setup. RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks.This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk.
Hardware RAID controllers and software RAID implementations are designed to recognise a drive which does not respond within a few seconds, and mark it as unreliable, indicating that it should be withdrawn from use and the array rebuilt from parity data. This is a long process, degrades performance, and if more drives fail under the resulting ...
RAID stands for redundant array of independent disks (or, formerly, redundant array of inexpensive disks). RAID levels may refer to: Standard RAID levels, all the RAID configurations defined in the Common RAID Disk Drive Format standard, which is maintained by the Storage Networking Industry Association
RAID; Erasure Coding; While technically RAID can be seen as a kind of erasure code, [5] "RAID" is generally applied to an array attached to a single host computer (which is a single point of failure), while "erasure coding" generally implies multiple hosts, [3] sometimes called a Redundant Array of Inexpensive Servers (RAIS). The erasure code ...
RAID 01, also called RAID 0+1, is a RAID level using a mirror of stripes, achieving both replication and sharing of data between disks. [3] The usable capacity of a RAID 01 array is the same as in a RAID 1 array made of the same drives, in which one half of the drives is used to mirror the other half.
RAID 5E, RAID 5EE, and RAID 6E (with the added E standing for Enhanced) generally refer to variants of RAID 5 or 6 with an integrated hot-spare drive, where the spare drive is an active part of the block rotation scheme. This spreads I/O across all drives, including the spare, thus reducing the load on each drive, increasing performance.
Error-correcting codes are used in lower-layer communication such as cellular network, high-speed fiber-optic communication and Wi-Fi, [11] [12] as well as for reliable storage in media such as flash memory, hard disk and RAM. [13] Error-correcting codes are usually distinguished between convolutional codes and block codes: