The term RAID stands for “Redundant Array of Independent Disks,” and it is a way for computer users to gain a lot of storage reliability from ordinary disk drives without having to resort to more expensive components. Better performance and/or capacity is achieved by arranging the disks into arrays consisting of two or more disks. The most commonly used RAID levels are RAID 0, 1, 5, 10, and 50. These are standard RAID levels used for most applications.
RAID 0 is known as a striped set, and works by evenly splitting data across two or more disks with no data redundancy. A RAID 0 can be created with disks of different sizes, although the usable storage space of each disk is limited to the size of the smallest disk to ensure proper performance. The advantage of a RAID 0 array is increased performance, especially in applications where data integrity is not critical. There is no fault tolerance with RAID 0, meaning if one drive fails, then all data is lost!
RAID 1 works by creating a mirror copy of data from one disk to another. This can be useful in applications where redundancy and read performance. As with RAID 0, the capacity of the storage space is limited to the size of the smallest disk, this time for proper redundancy.
RAID 5 works as a striped set with distributed parity (copies of data spread across multiple disks). In the event of the failure of one disk, the data remains unaffected unless a second drive fails. RAID 5 will suffer reduced performance until the failed drives are replaced. RAID 6 is similar to RAID 5, but this level adds an additional parity block, using two parity blocks spread over all the other disks. RAID 6 offers more protection against data loss when used in large arrays, especially when the potential for data loss is greater in these large arrays.
RAID 10, sometimes known as RAID 1+0, is used for high load databases thanks to faster speeds with such a setup. Like all other RAID sets, the usable per-disk capacity for a RAID 10 array is still the smallest disk drive in the array. RAID 50 combines straight block-level striping found in RAID 0 with the distributed parity of RAID 5, while RAID 60 combines distributed double parity found in RAID 6 with the striping of RAID 0.