What is RAID

RAID stands for Redundant Array of Independent Disks (full form of raid). RAID is a method of combining several hard disks into one unit or group.It is a data storage Virtualization technology that combines multiple disk components into a logical unit for the purposes of data redundancy or performance improvement. It also offers fault tolerance role and higher throughput levels than a single hard disk or group of independent hard disks. RAID levels 0, 1, 5, 6 and 10 are the most popular configurations.

RAID Step and Configurations


RAID 0 splits data across disks, resulting in higher data throughput. The performance of this configuration is extremely high, but a loss of any disk in the array will result data loss. This level is commonly known to as striping. Minimum number of disks required are: 2 Performance: High Redundancy: Low Efficiency: High	Advantages: High performance Easy to implement Highly efficient (no parity overhead) Disadvantages: No redundancy Limited business use cases due to no fault tolerance

RAID 1 writes all data to two or more disks for 100% redundancy: if either disk fails, no data is lost. Compared to a single disk, RAID 1 tends to be fast on reads, slow on writes. This is a good entry-level redundant configuration. However, since an entire disk is a duplicate, the cost per MB is high. This is commonly known to as mirroring. Minimum number of disks required are: 2 Performance: Average Redundancy: High Efficiency: Low	Advantages: Fault tolerant Easy to recover data in case of disk failure Easy to implement Disadvantages: Highly inefficient (100% parity overhead) Not scalable (becomes very costly as number of disks increase)

RAID 5 stripes data in a block level across several disks, with parity equality distributed among the disks. The parity information allows recovery from the failure of any single disk. Write performance is rather quick, but due to parity data must be skipped on each disk during reads, reads are slower. The low ratio of parity to data means low redundancy overhead. Minimum number of disks required are: 3 Performance: Average Redundancy: High Efficiency: High	Advantages: Fault tolerant High efficiency Best choice in multi-user environments which are not write performance sensitive Disadvantages: Disk failure has a medium impact on throughput Complex controller design

RAID 6 is an upgrade version from RAID 5: data is striped in a block level across several disks with double parity distributed among the disks. As in RAID 5, parity information allows recovery from the failure of any single disk. The double parity gives RAID 6 additional redundancy at the cost of lower write performance (read performance is the same), and redundancy overhead remains low. Minimum number of disks required are: 4 Performance: Average Redundancy: High Efficiency: High	Advantages: Fault tolerant – increased redundancy over RAID 5 High efficiency Remains a great option in multi-user environments which are not write performance sensitive Disadvantages: Write performance penalty over RAID 5 More expensive than RAID 5 Disk failure has a medium impact on throughput Complex controller design

RAID 0+1 is a mirror (RAID 1) array whose segments are striped (RAID 0) arrays. This configuration combines security of RAID 1 with an extra performance boost from the RAID 0 striping. Minimum number of disks required are: 4 Performance: Very High Redundancy: High Efficiency: Low	Advantages: Fault tolerant Very high performance Disadvantages: Expensive High Overhead Very limited scalability

RAID 10 is a striped (RAID 0) array whose segments are mirrored (RAID 1). RAID 10 is a popular configuration for today environments where high performance and security are required. In terms of performance it is similar to RAID 0+1. However, it has superior fault tolerance and rebuilds performance. Minimum number of disks required are: 4 Performance: Very High Redundancy: Very High Efficiency: Low	Advantages: Extremely high fault tolerance – under certain circumstances, RAID 10 array can sustain multiple simultaneous disk failure Very high performance Faster rebuild performance than 0+1 Disadvantages: Very expensive High overhead Limited scalability

RAID 50 combines RAID 5 parity and stripes it as in a RAID 0 configuration. But high in cost and complexity, performance and fault tolerance are superior to RAID 5. Minimum number of disks required are: 6 Performance: High Redundancy: High Efficiency: Average	Advantages: Higher fault tolerance than RAID 5 Higher performance than RAID 5 Higher efficiency than RAID 5 Disadvantages: Very expensive Very complex / difficult to implement

RAID 60 combines RAID 6 double parity and stripes it as in a RAID 0 configuration. Although high in cost and complexity, performance and fault tolerance are superior to RAID 6. Minimum number of disks required are: 8 Performance: High Redundancy: High Efficiency: Average	Advantages: Higher fault tolerance than RAID 6 Higher performance than RAID 6 Higher efficiency than RAID 6 Disadvantages: Very expensive Very complex / difficult to implement