In
computing, the
acronym RAID (originally
redundant array of inexpensive disks, now also known as
redundant array of independent disks) refers to a
data storage scheme using multiple
hard drives to share or replicate
data among the drives. Depending on the configuration of the RAID (typically referred to as the RAID level), the benefit of RAID is one or more of increased
data integrity,
fault-tolerance,
throughput or
capacity compared to single drives. In its original implementations, its key advantage was the ability to combine multiple low-cost devices using older technology into an array that offered greater capacity, reliability, speed, or a combination of these things, than was affordably available in a single device using the newest technology.
At the very simplest level, RAID combines multiple hard drives into a single logical unit. Thus, instead of seeing several different hard drives, the
operating system sees only one. RAID is typically used on
server computers, and is usually (but not necessarily) implemented with identically sized disk drives. With decreases in hard drive prices and wider availability of RAID options built into
motherboard chipsets, RAID is also being found and offered as an option in more advanced personal computers. This is especially true in computers dedicated to storage-intensive tasks, such as video and audio editing.
The original RAID specification suggested a number of prototype "RAID levels", or combinations of disks. Each had theoretical advantages and disadvantages. Over the years, different implementations of the RAID concept have appeared. Most differ substantially from the original idealized RAID levels, but the numbered names have remained. This can be confusing, since one implementation of RAID 5, for example, can differ substantially from another. RAID 3 and RAID 4 are often confused and even used interchangeably.
The very definition of RAID has been argued over the years. The use of the term
redundant leads many to object to RAID 0 being called a RAID at all. Similarly, the change from
inexpensive to
independent confuses many as to the intended purpose of RAID. There are even some single-disk implementations of the RAID concept. For the purpose of this article, we will say that any system which employs the basic RAID concepts to combine physical disk space for purposes of reliability, capacity, or performance (or even sociability — see the
Just a Bunch Of Disks discussion) is a RAID system.
