RAID stands for Redundant Array of Inexpensive Disks. RAID is a technology that is used to increase the performance and/or reliability of data storage. A RAID system consists of two or more drives working in parallel.
1. RAID level 0 – Striping
In a RAID 0 system data are split up into blocks that get written across all the drives in the array. The RAID technology is easy to implement.
2.RAID level 1 – Mirroring
Data are stored twice by writing them to both the data drive (or set of data drives) and a mirror drive (or set of drives). In case a drive fails, data do not have to be rebuild, they just have to be copied to the replacement drive.
3. RAID level 5
RAID 5 is the most common secure RAID level. It requires at least 3 drives but can work with up to 16. Data blocks are striped across the drives and on one drive a parity checksum of all the block data is If a drive fails, you still have access to all data, even while the failed drive is being replaced and the storage controller rebuilds the data on the new drive. It is best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented.
4. RAID level 6 – Striping with double parity
RAID 6 is like RAID 5, but the parity data are written to two drives. That means it requires at least 4 drives and can withstand 2 drives dying simultaneously. If two drives fail, you still have access to all data, even while the failed drives are being replaced. So RAID 6 is more secure than RAID 5.
5. RAID level 10 – combining RAID 1 & RAID 0
It is possible to combine the advantages (and disadvantages) of RAID 0 and RAID 1 in one single system. This is a nested or hybrid RAID configuration. If something goes wrong with one of the disks in a RAID 10 configuration, the rebuild time is very fast since all that is needed is copying all the data from the surviving mirror to a new drive. This can take as little as 30 minutes for drives of 1 TB.