Redundant array of independent disks (RAID) is a method of storing duplicate data on two or more hard drives. There are several RAID types:
RAID 0 is a standard RAID. It also called disk striping. However, it is not redundant normally used to increase the performance of systems that rely heavily on RAID for their operations. It is also used to create a few large logical volumes from multiple sets of smaller capacity physical drives.
It is also called RAID-I. Disk mirroring is a form of disk backup in which anything that is written to a disk is simultaneously written to a second disk. If a physical hardware failure occurs in a disk system, the data is not lost, as the other hard disk contains an exact copy of that data. Disk mirroring can be done either hardware or software based.
Disk duplexing is a variation of disk mirroring in which each of multiple storage disks has its own SCSI controller. Mirroring provides data protection in the case of disk failure, because data is constantly updated to both disks. However, redundant controllers enables continued data access in case of one of the controller fails.
RAID-5 is a block-level data striping and distributes parity to all the disks. There is still some overhead during parity calculations, but since parity is written to all disks, no single drive can be considered the bottleneck, and I/O operations are spread evenly across all drives. RAID-5 requires at least three and usually five disks for the array. It’s best for multi-user systems in which performance is not critical or which do few write operations.
This type is similar to RAID-5 but includes a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance.
Combining RAID-0 and RAID-1 is often referred to as RAID-10, which offers higher performance than RAID-1 but at much higher cost. There are two subtypes: In RAID-0+1, data is organized as stripes across multiple disks, and then the striped disk sets are mirrored. In RAID-1+0, the data is mirrored and the mirrors are striped.