RAID ControllerRAID system is group of multiple hard disk drives that functions as a single storage device. To manage and control multiple hard disks as a single storage device RAID controllers are used. RAID controllers use different techniques or protocols to obtain their task. There are many techniques that RAID controller use. However RAID 0, RAID 1, and RAID 5 are the most commonly used types.

RAID Controller Types

RAID controllers are avail be as both internal and external modules. As internal RAID controllers are buses or cards. Externally RAID controllers are available as peripheral devices.

Bus based / computer board RAID controllers

RAID controller computer boards or cards are similar to expansion cards. These are installed into server systems or PCs. RAID controller cards are quite suitable for lower-end systems. Array of hard disks is connected to it. RAID controller offers its services just as SCSI adapter host adapter or ATA / IDE controller. RAID controller card uses SCSI or IDE / ATA standards to interface with disks. Therefore such devices are also known as SCSI RAID controllers, PCI RAID Controllers, or SCSI host RAID controllers. Controller sends the data to the other components through system bus (PCI, ISA).

Integrated RAID Controllers

Motherboards designed for server systems usually contain integrated RAID controller drivers. These integrated RAID controller drivers serve same as bus based cards. These also reduce the overall cost but offer less flexibility.

External RAID Controllers

External RAID controllers are peripheral devices that are available as standalone boxes. Such configuration is suitable for high-end system designs. The box contains the array of hard disk. Box can be connected to the server or PC. Within the box the RAID controller uses SCSI to control and manage the hard disks.

RAID Levels

RAID levels define different techniques to control data among drives. There are several RAID levels but RAID 0, 1, and 5 are common. Moreover nested RAID levels are also implemented. For example RAID 10 is the combination of RAID 0 and RAID 1.

RAID 0

RAID 0 level is also known as striped set. RAID 0 splits data evenly among hard disks in the RAID system. RAID 0 is non-redundant, as it offers no parity information. Such technique increases performance and allows creating small number of large virtual disks. Drawback is failure of any of the disks causes complete data loss.

RAID 1

RAID 1 level exact copy of data is created on two or more disks. This improves the read performance but affects capacity. Also such technique causes redundancy due to duplication of data.

RAID 2

RAID 2 implements hamming codes for error correction stripping data at bit level. This technique is suitable for the drives that do not have built-in error detection. This technique is not currently used.

RAID 3 & RAID 4

In RAID 3 implementation byte level stripping is used. This is not a good technique and very rare to use. It cannot serve multiple requests. RAID 4 is similar to RAID 3 but it uses block level stripping.

RAID 5

RAID 5 also uses block level stripping. It distributes the parity among all the member drives. Due to its lower cost of redundancy the RAID 5 implementation is the most popular.