RAID stands for Redundant Array of Independent Devices or sometimes also referred to Redundant Array of Inexpensive Devices. RAID is a storage technology that combines multiple disk drive components into a logical unit. For this reason RAID comprises of at least two hard disk drives. Depending upon RAID implementation data is distributed across the drives in one of many ways called â€˜RAID levelsâ€™. This implementation depends on the level of redundancy and performance required.
PURPOSE OF RAID:-
RAID is used to make data redundant, this redundancycan be used in fault tolerance and as a performance enhancer. RAID devices help in fault tolerance by duplicating data, this ensure backup in case of disk failure. Although the use of RAID for fault tolerant is limited until the hard disk containing backup is compromised. For instance, in case of failure of a hard disk drive RAID allows us to retrieve data from backup drive and also in some of the RAID levels replaces bad drives with spare drives but it does not provides us safety of data when backup drive gets failed for example in case of fire. Also it greatly improves read/write performance. The term â€˜inexpensiveâ€™ in the acronym RAID is used because RAID technology provides a cost effective method to achieve the above stated.
For instance, improved performance can be achieved by buying better and faster hard disks and replacing the old ones but that is costly, RAID on the other hand achieve the same with only a software installation required.
TYPES OF RAID:-
Software based RAID
Disks attached to servers can be turned into RAID arrays using â€œmdadmâ€ software on linux operating systems, thus it is called software based RAID. Software RAID does its processing on the server motherboard, adding to the processing load and thus slows down the operations on that device. As the software used to configure RAID is dependent on OS , so it canâ€™t be generally used for partitions that are shared between operating systems.
Hardware based RAID
Hardware RAID is configured directly on motherboard of servers or implemented as separate RAID cards and controlled by a RAID controller. As processing work is done on separate controller card there is no added load to server processes and buses. Hardware RAID are more expensive than software RAID.