(redundant array of independent disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, input/output operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly increases fault-tolerance.
Redundant Array of Independent/Inexpensive Disks/Devices) – A method of providing data redundancy, improved performance and/or quick data recoverability from disk crashes, by spreading or duplicating data across multiple disk drives. Commonly used RAID types include RAID 0 (Data Striping), RAID 1 (Disk Mirroring) and RAID 5 (Striping with Distributed Parity). RAID configurations typically require SCSI disk drives (not IDE/EIDE) and may require identical drives (same capacity, brand, etc.). RAID arrays appear to the operating system as a single device.