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Big Computer 3 is one year old! - part 4 of 1 2 3 4 5 6

by Mike McNamee Published 01/06/2009

RAID stands for Redundant Array of Inexpensive Disks. There are many ways to set up a RAID array but you always require more than one hard drive; some of the set-ups have only slight variations. RAID types vary from RAID 0 to RAID 10. For want of space we will only describe three types here.

RAID 0

RAID 0 uses a method of writing to the disks called striping. Let's assume you have a server with three drives of 500 MB, 1 GB and 2 GB. Normally a server would treat each of these drives individually. By incorporating striping, the system would see all of the drives as only one drive for a total of 3.5 GB. When the system writes data to the disk, the RAID 0 striping kicks in and automatically distributes the data across all three drives. Part of a file (chunks of data) will be written to the first drive, the next part to the second drive, the next part to the third drive and then it starts all over again until the entire contents of the file have been written. This increases speed but you have an increased risk of a failure and no redundancy. Speed goes up by 25% to 30%.

RAID 1

RAID 1 uses a technology called mirroring or disk shadowing. RAID 1 requires a minimum of two drives that are exactly the same size. Every time a write is executed the same data is written to both drives, ie a mirror image. So what you achieve with RAID 1 is data redundancy. If one of the drives fails, the system can continue to run by just writing to one drive. If you have hot swappable drives, you could pull out the bad drive, plug in a new one and the system is back to its normal state. How efficient and easy it is to do all of this depends on the RAID controller and/or software that is being used. There is no change in speed and you lose half your disk capacity.

RAID 5

RAID 5 accomplishes both techniques of RAID 0 and RAID 1. RAID 5 requires a minimum of three drives and it is recommended that all drives on the system be of the same size. The more drives you have on the server, the better RAID 5 will perform. Five is a recommended number This will allow for up to two drives to fail and the system can keep running

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1st Published 01/06/2009
last update 21/07/2022 08:46:23

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