Introduction Volume Sets Striped Partitions Striped Sets With Parity Disk Mirroring Disk Duplexing RAID 0 RAID 1 RAID 2 RAID 3, 4 RAID 5 Overview
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The word "redundant" means an unnecessary repetition.

The word "array" means a lineup.

A Redundant Array of Independent Disks (originally known as Redundant Array of Inexpensive Disks) is essentially where a network file server uses extra disks to keep multiple copies of data.

In these situations, the data itself is more valuable than the cost of the disks. That's why the disks were termed inexpensive.

Making repeated copies of the valuable data isn't actually unnecessary; still, that's what the computer people called it, using the word "redundant."

The concept of RAID data protection has been around long enough that there are now six different levels of protection (0 through 5). Each level indicates a higher degree of protection.