A Brief Info About RAID – Levels

A Brief Info About RAID – Levels

Monday, September 19th, 2011

What is RAID ?

RAID basically an abbreviated term that refer to Redundant Array of Independent Disks. They are used for achieving a high level of redundancy or fault tolerance. Multiple disk drives are used in combination inorder to achieve a proper distribution of data across the drives. Various architectures of RAID may be used based on the requirements and are known as the RAID arrays. Different architectures offer different levels of data reliability and input/output performance.

The following is a list of RAID configurations that are used in the Industry :

RAID 0 – Striped Disk Array without Fault Tolerance
It offers data striping and lack the aspect of redundancy. Users can experience an improvement in performance but have to compromise on fault tolerance. In this if one drive fails the complete data within the array gets lost.

RAID 1 – Mirroring and Duplexing
Mirroring is a key benefit offered by RAID 1. In this, the seamless and simultaneous copying of information between disks is carried out hence the term replication or mirroring. In this kind of RAID configuration if any disk-drive faces a malfunction, the data isn’t lost, you’d still be able to work as normal. Replacing the faulty drive with a new one should get you back in perfect shape.the  one disk gets fried, the other can keep working. There is a requirement of atleast two drives for setting up a RAID 1 configuration.

RAID 3 – Bit-Interleaved Parity
It offers a dedicated parity with a byte level striping. It lacks the capability of executing simultaneous requests, hence is seldomly used.

RAID 4 – Dedicated Parity Drive
It shares similarity with RAID3 but with a difference that the disk striping done.

RAID 5 – Block Interleaved Distributed Parity
It is a widely preferred RAID configuration for business servers and enterprise NAS devices. With this type of configuration data and parity are striped across three or more disks hence resulting in optimum performance and good fault tolerance.

RAID 7 is a proprietary level of RAID that was owned by Storage Computer Corporation, which is no more in business now.

RAID 0+1 – A Mirror of Stripes
Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. RAID 0+1 is a mirrored array with segments which are RAID 0 arrays. It offers replication and sharing of data among disks. It is only used over particular infrastructures which offers high performance, though the scalability may be compromised to a certain extent.

RAID 10 – A Stripe of Mirrors
It is a combination of RAID 1 and 0. It is a blend of mirroring offered by RAID 1 and striping offered by RAID 0. A minimum of four disks are required for setting up this Raid Level.

Note : RAID 2 and 4 are very rarely used these days.

Author of the Article : Stanley Jones from Eukhost Ltd.

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