RAID - Redundant Array of Independent Disks
RAID stands for Redundant Array of Independent Disks. RAID is a system, which uses several hard disks for replicating data between the hard disks. The basic idea behind RAID is combining multiple hard disks into a single logical unit. When RAID is implemented, the operating system sees the array of disks as one drive. RAID systems are commonly implemented with hard disks with the same size.
RAID systems are relatively expensive (they are becoming more affordable lately), that’s why they are implemented mostly in mission-critical server environments, where the data protection and integrity are of higher importance.
IBM patented RAID in 1978. Ten years later Paterson, Gibson and Katz defined the RAID levels from 1 to 5 in their “A Case for Redundant Arrays of Inexpensive Disks (RAID)” paper. Note that the paper title uses the word “Inexpensive” instead of “Independent”, because at that time this was the idea behind RAID – providing inexpensive data storage with higher level of reliability.
RAID can be implemented with specialized RAID hardware or with RAID software running on standard hardware.