RAID is the acronym for Redundant Array of Independent Disks. It is a technology that provides increased input/output speed and/or reliability by combining multiple hard drives into a logical unit where all drives in the array are interdependent.
RAID is now used as an general term for computer data storage schemes that can divide and replicate data among multiple disk drives. The schemes or architectures are named by the word RAID followed by a number (e.g., RAID 0, RAID 1). The various designs of RAID systems involve two key goals: increase data reliability and increase I/O performance. In the setting of RAID 0, the I/O speed is emphasized by treating all drives as one single disk without any redundancy in data. The system will fail if any one of the hard drives corrupted, although the I/O speed may be twice or more than a single hard drive. Contrast to RAID 0, the RAID 1 setting emphasizes the redundancy instead of I/O speed. It basically duplicates all data to all disks. As long as one of the hard drives survives, the data can be recovered. Other RAID settings are somewhere in between to seek for the balance between data redundancy and I/O speed.