RAID

RAID is an acronym that stands for Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks. RAID is a term used in computing. With RAID, several hard disks are made into one logical disk. There are different ways this can be done. Each of the methods that puts the hard disks together has some benefits and drawbacks over using the drives as single disks, independent of each other. The main reasons why RAID is used are:

• To make the loss of data happen less often. This is done by having several copies of the data.
• To get more storage space by having many smaller disks.
• To get more flexibility (Disks can be changed or added while the system keeps running)
• To get the data more quickly.

It is not possible to achieve all of these goals at the same time, so choices need to be made.

There are also some bad things:

• Certain choices can protect against data being lost because one (or a number) of disks failed. They do not protect against the data being deleted or overwritten, though.
• In some configurations, RAID can tolerate that one or a number of disks fail. After the failed disks have been replaced, the data needs to be reconstructed. Depending on the configuration and the size of the disks, this reconstruction can take a long time.
• Certain kinds of errors will make it impossible to read the data

Most of the work on RAID is based on a paper written in 1988.^[1]

Companies have used RAID systems to store their data since the technology was made. There are different ways in which RAID systems can be made. Since its discovery, the cost of building a RAID system has come down a lot. For this reason, even some computers and appliances that are used at home have some RAID functions. Such systems can be used to store music or movies, for example.

1. ↑ ""A Case for Redundant Arrays of Inexpensive Disks" - Patterson, Gibson, Katz" (PDF). University of California. 1988.