RAID

RAID is an acronym for Redundant Arrays of Inexpensive Disks. These provide a mechanism for load balancing and securing your data across multiple disks.

There are three terminology related to RAID, that is

1. Striping : It is the process of breaking data into pieces and distributing across multiple disk that supports a logical volume. It yeilds better Performance.

2. Mirroring : Its the process of writting the same data simultaniously to another member of the same volume.Mirroring provides protection for data by writting exactly same data to other members in the same volume.

3. Parity : Its the error checking.

Types of RAID

1.Host Based RAID: RAID can be software based.its imposes a small overhead as it consumes memory, I/O bandwidth, and CPU space on the host where it is implemented.

2.Embedded Controller based RAID : RAId implemented by hardware is in the form of micro code present in dedicated disk controler module that connect to the host this type of RAID is know as Embedded Controller based RAID .

3.Bridge based RAID : RAID can also be implemented using controllers that are external to the host where it is implemented. This type of RAID are known as bridge based RAID.

RAID Levels:
Initially RAID was a simple method of logically joining two or more disks.RAID levels usually range from 0 to 7.

RAID 0: Plain striping

RAID 1: plain mirroring

RAID 0+1 / 1+0 : combination of 0 and 1- striping and then mirroring or vice versa

RAID 2: Early implementation of striping with parity

RAID 3 : Striping with bit/byte level parity,dedicated parity disk

RAID 4: Striping with block level parity

RAID 5: Striping with block level parity, distributed parity across the number of disks in volume

RAID 6: Striping with block level multidimensional parity

RAID 7: Same as RAID 3 but with better asynchronous capability for read and write.

RAID s : EMC's implementation of RAID 3/5

Auto RAID : HP's automatic RAID technilogy.