What is a "RAID" hard drive?
RAID is an acronym for redundant array of inexpensive disks or redundant array of independent disks. It is a technology that provides increased storage reliability through redundancy, combining multiple low-cost, less-reliable disk drives components into a logical unit where all drives in the array are interdependent. This concept was first defined by David A. Patterson, Garth A. Gibson, and Randy Katz at the University of California, Berkeley in 1987 as a redundant array of inexpensive disks. Marketers representing industry RAID manufacturers later reinvented the term to describe a redundant array of independent disks as a means of dissociating a low-cost expectation from RAID technology.
RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. The different schemes or architectures are named by the word RAID followed by a number (e.g. RAID 0, RAID 1). RAID's various designs involve two key design goals: increase data reliability and/or increase input/output performance. When multiple physical disks are set up to use RAID technology, they are said to be in a RAID array.[3] This array distributes data across multiple disks, but the array is seen by the computer user and operating system as one single disk. RAID can be set up to serve several different purposes.
RAID drives can be configured in a parallel manner thereby increaseing performance. Data is written to or read from all the drives in the array simultaneously making the system behave as if it had a single, lightning fast hard drive. Or they can be set up so that data is automatically mirrored or written to multiple drives simultaneously thereby improving reliability. If a hard drive fails in a non-mirrored system, data will almost certainly be lost. If a hard drive fails in a mirrored system, the remaining drive which contains a complete copy of all the data provides uninterrupted service. The failed hard drive can then be replaced without loss of data.
