page_title: RAID
section_title: Why use RAID?
hierarchical_section_title: RAID / Introduction / Why use RAID?
caption_attribution_description: English: Front view (cropped) of four hard disks forming a RAID array. This array is inside a desktop system, using a common controller. The blue levers allow to remove/replace a single harddisk while the system keeps running. Deutsch: Mehrere Festplatten eines RAID verbundes. Diese sind in einem Desktopcomputer eingebaut. Dieses System verkraftet den Austausch einer Platte im laufenden Betrieb.
context_page_description: 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
  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 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.
context_section_description: One of the reasons why many companies are using RAID is that the data in the array can simply be used. Those using the data need not be aware they are using RAID at all. When a failure occurred and the array is recovering, access to the data will be slower. Accessing the data during this time will also slow down the recovery process, but this is still much faster than not being able to work with the data at all.
  Depending on the RAID level however, disks may not fail while the new disk is being prepared for use. A disk failing at that time will result in losing all the data in the array.
  The different ways to join disks are called RAID levels. A bigger number for the level is not necessarily better. Different RAID levels have different purposes. Some RAID levels need special disks and special controllers.
caption: Close up of 4 disks that make a RAID array, built into a desktop system. The blue latches allow for the exchange of the disks while the system keeps running.
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