Posted on 16 April 2007 @ 23:23

In the Storage forum you'll read a lot of about RAID. This topic will explain in a nutshell what RAID is and explains the different RAID levels.

What is RAID?
RAID is an acronym for Redundant Array of Independent Disks, it's a technique that allows to combine harddrives into one big virtual harddrive, either for increased speed or better reliability. The features of RAID depend on the RAID level, which tells us which technique is used to combine the disks. They are:

RAID0
Also called Striping. This RAID level is the fastest, it will put your data on all harddisks in the RAID0 set which allows huge performance improvements. Theoretically, a RAID0 volume consisting of 2 harddrives is twice as fast as a single harddrive. The downside though, is that RAID0 does not offer any protection against drive failure. Worse, if one drive in the set fails, all data on all harddrives within the set is lost. Therefore, RAID0 requires that either your data is expendable or that you create and maintain proper backups.

RAID1
Also called Mirroring. Maintains a live-backup, so when using 2 harddrives the second one is mirroring the first. When you write to the RAID volume, data is written to both drives. This way, when one drive fails you have an exact copy of your data on the second drive, improving reliability and data security. The downside is that RAID1 offers little performance improvement and is considered the slowest RAID-level.

RAID5
Also called Parity RAID. This level is a complex one, and is not seen often except on hardware controllers for just this reason. Today this level is implemented on some onboard controllers though, while their implementation remains weak it offers two major benefits: data security and low overhead. A RAID5 volume will 'waste' fewer room. With 8 disks, using RAID1 you can effectively use only 4 of them to store data. With RAID5 you can use 7; you'll only sacrifice one drive in order to achieve data security. If one drive fails, you keep all data. But, if another fails, you loose all. This RAID-level is often used to store huge amounts of data while protecting the data from drive failure.

Combinations of levels are also possible, like a RAID10 volume (RAID1 + RAID0) of RAID50 (RAID5 + RAID0).

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