Tuesday, June 12, 2012

RAID Levels

What is RAID?
Redundant Array of Independent Disks, it uses multiple harddrive to store the data. Even if one drive is failed the data is safe and accessible.

Where it uses?
RAID can be used in critical applications where you feel data is more important. This helps to controls the data loss of any business and to recover from disaster.To implement RAID we should have more than one disk

Terminology of RAID
a) Mirroring – Data will be written into multiple disks, ie., copy of data will be maintained.
b) Striping – Sequential blocks of data will be splitted into multiple disks.
c) Fault Torence – Parity information will be stored in this type of RAID mechanism, even if one disk will fail it will allow recovering the data.

Levels of RAID

RAID -0 – Data is simply written using a striping mechanism, that means sequential data blocks will be written into multiple hard drives simultaneously. It will provide huge performance, but the downside of this RAID0 is if one of the drive fails all data is lost. It offers only speed not data protection. So be careful while choosing it.
RAID -1 – This utilizes mirroring mechanism while writing data into disks, that means same data will be maitained at two places, if one drive fails we can access the data from other drives. But the downside of this mechanism is out of two drives we can make use of only one, that means the usable capacity of the drives is only 50%
RAID – 5 – It uses a mechanism called fault tolerance that data will be written into all the drives with extra information called parity bit information. This will be used to retrieve information from any one the drive fails. To implement RAID-5 it requires minimum of 3 drives, out of which 2 drives can be used to write data and 1 will be used to store parity information. 
RAID – 6 – It is similar to RAID -5 but it provides high fault tolerance, data can be written into all drives with parity information, if any of two hard drives fail we are in a position to retrieve data from the others, but it requires minimum of 4 drives and the usable capacity is only 2 drives out of 4 drives.
RAID – 10 – It’s a combination of RAID 1 and RAID 0, in this mechanism data will be mirrored and striped across the drives, the usable capacity is 50% only. It provides performance as well as data protection.

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