Thursday, 16 May 2013

Raid Levels

The different raid levels available today

Raid 0 - Stripping data across the disks. This stripes the data across all the disks present in the array. This improves the read and write performance. Eg. Reading a large file takes a long time in comparison to reading the same file from a Raid 0 system.They is no data redundancy in this case.

Raid 1 - Mirroring. In case of Raid 0 it was observed that there was no redundancy,i.e if one disk fails then the data is lost. Raid 1 overcomes that problem by mirroring the data. So if one disk fails the data is still accessible through the other disk.

Raid 2 - RAID level that does not use one or more of the "standard" techniques of mirroring,striping and/or parity. It is implemented by splitting data at bit level and spreading it across the data disks and redundant disk. It uses a special algorithm called as ECC (error correction code) which is accompanied across each data block. These are tallied when the data is read from the disk to maintain data integrity.

Raid 3 - data is striped across multiple disks at a byte level. The data is stripped with parity and the parity is maintained in a separate disk. So if that disk goes off , it results in a data loss.

Raid 4 - Similar to Raid 3 the only difference is that the data is striped across multiple disks at block level.

Raid 5 - Block-level striping with distributed parity. The data and parity is stripped across all disks thus increasing the data redundancy. Minimum three disks are required and if  any one disk goes off the data is still secure.

Raid 6 - Block-level striping with dual distributed parity. Its stripes blocks of data and parity across all disks in the Raid except that it maintains two sets of parity information for each parcel of data thus increasing the data redundancy. So if two disk go off the data is still intact.

Raid 7 - Asynchronous, cached striping with dedicated parity. This level is not a open industry standard. It is based on the concepts of Raid 3 and 4 and a great deal of cache is included across multiple levels. Also there is a specialized real time processor to manage the array asynchronously.

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