raid

RAID is an orchestrated approach to computer data storage in which data is written to more than one secondary storage device. Instead of storing all data in a single hard disk drive or solid-state drive, RAID coordinates two or more such devices into a disk array. When the computer writes data to secondary storage, the RAID system distributes the data across the array. There are several possible ways of doing this, and those various configurations are called RAID levels.
RAID levels are distinguished by the amount of redundancy they afford and the minimum number of drives they require, as well as by their relative complexity, performance, energy efficiency, fault tolerance, and availability. The definitive techniques used by RAID were conceived in the 1970s and 1980s: data striping to improve read/write efficiency, and disk mirroring or parity drives for data recovery. With the exception of RAID 1, all of the standard RAID levels use storage virtualization to abstract multiple storage devices into one logical storage volume.
In its original coinage, RAID is an acronym for redundant array of inexpensive disks. The RAID Advisory Board (est. 1992) later redefined the acronym to mean redundant array of independent disks. Before the advent of data striping and redundant, online disks, it was common for high-capacity, high-availability data storage to rely on so-called SLEDs ("single, large, expensive disks") connected to mainframe computers. RAID has been deployed not only in mainframe computers, but in personal computers, supercomputers, file servers, database servers, web servers, and network-attached storage appliances.

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