RAID – What is it and what are the differences?

RAID is a method of storing data on multiple hard disks. Through the “magic” of the disk array, all of the individual disks appear as a single disk to the operating system. Large arrays can be split into smaller logical disks, that can be any size up to the total amount of disk space. Depending on exactly how the data is spread across the multiple disks determines the relative speed and security of the data on the disks.

Back in the old days when large (750MB) hard disks were relatively expensive (say $1200 US) and smaller disks (100MB) were relatively inexpensive (maybe $130), somebody figured out that it could be possible to link several of the inexpensive disks together to roughly equal the capacity of a single larger disk. The complete package was called a disk array, and the method of storing the data on the disks was called RAID, for Redundant Array of Inexpensive Disks.

Today, the relative price difference between an 80GB and a 160GB or even a 400GB hard drive is not so great; however, RAID is still very much a part of life with computers—especially with servers. Obviously there is more to RAID than just a cost savings. (RAID now stands for Redundant Array of Independent Devices, which indicates the drift away from price being the motivating factor in choosing a RAID solution.) In fact, by the time you factor in the additional hardware to create and manage the array, RAID usually costs more than non-RAID solutions. So why do we use it? The answers are speed and reliability.

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