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Different Types if RAID Levels
Today, the common types of RAID used are RAID 0, RAID 1, RAID 1+0, RAID 5 and RAID 6. It is rather sufficient for us to cover these in brief to gain a better understanding of how RAID works.
RAID 0 - Data stripping with no parity or fault tolerance. It is used to increase system performance because N-disks RAID 0 array theoretically provides N times read and write speed improvement comparing to a single disk. If any one of the disks fails, recovery is difficult and only limited to data size less than the strip block size.
RAID 1 is also called disk mirroring, usually comes in a pair of disks. It is used for critical system processing which tolerates zero down time. However, it has 100% wastage in disk space but recovery is relatively easy. Should one of the disks fails, data can be easily copied from the other working disk.
RAID 1+0, as some call it RAID 10. It uses a combination of mirroring and striping above to enjoy the benefits of both worlds. It has the featue of fault tolerance and enhanced read write performance. The array inherits RAID 1 fault tolerance and RAID 0 speed efficiency. The system array can withstand single disk to multiple disk failures, as long as at least one of the mirrored pair survives.
RAID 5 is one the most commonly used type. It impements stripe sets with parity. Stripping increase IO throughput while parity provides fault tolerance against single disk failure. It is capable of reconstructing the data from a single failed disk by using the parity data and data from other member disk through XOR function. In terms of disk space resources, it has the least wastage as it only takes up the capacity of one disk member. Compared to RAID 0 and RAID 1, recovery of RAId 5 is more complicated as there are many different types of implementation of of RAID 5 parity layout.
RAID 6 is an improvement to RAID 5 by utilizing two different parity functions, thus enabling it to survive two hard drive failures. It also increases the disk space overhead to two member disks. Recovery if failed RAID 6 is more complex than the other RAID level and is less common in the market.