RAID is a way of distributing data on multiple (two or more) independent physical disks in order to realize enhanced data reliability and/or improved performance. The combined physical disks make up what is called an array. This array appears on the host system as a single disk. Arrays are also known as "virtual disks" or "container".
There are several different RAID levels or types, which determine how the data is stored in the array. Each level has specific data protection and system performance characteristics.
Benefits of RAID Implementation
In general, there are two benefits of creating RAID. Depending on which RAID level you use, the benefits include one or both of the following:
Faster I/O performance: In RAID 0 and RAID 10 arrays, disk striping allows you to write data across multiple physical disks instead of just one single physical disk. At the same time, the host system can access data from each physical disk simultaneously.
Higher data protection: In RAID 1 and RAID 10 arrays, the data is on disk mirroring. Besides, the data is also parity protected in RAID 5 array. Data loss caused by a physical disk failure can be recovered by rebuilding missing data from the remaining physical disks containing mirroring and parity.
Commonly Used RAID Levels
There are various combinations of these approaches giving different trade-offs of protection against data loss, additional storage, and performance, including RAID 0, RAID 1, RAID 2, RAID 3, RAID 4, RAID5, RAID 6, and RAID 10 (1+0). Among them, RAID levels 0, 1, 5 and 10 are the most commonly used, and cover most requirements.
RAID 0 - Striping without parity, good performance but no data redundancy.
RAID 1 - Mirroring without parity or striping, one-to-one redundancy for disk errors, and single disk failures.
RAID 5 - Striping with distributed parity (parity data across all physical disks), provides improved performance and high data redundancy.
RAID 10 - RAID 1 + RAID 0, mirroring combined with striping, best performance as well as fault tolerance for multiple drive failures.
The automated process of offering 100 percent data redundancy using two physical disks simultaneously, by maintaining an exact copy of one physical disk’s data on the second physical disk. If one physical disk fails, the contents of the other physical disk can be used to maintain the integrity of the system and to rebuild the failed physical disk.
Redundant information that is associated with a block of information and used to rebuild a disk that has failed. For example, a RAID 5 array maps data and parity intermittently across a set of physical disks. Within each stripe, the data on one disk is parity data and the data on the other disks is normal data. Therefore, a RAID 5 array requires at least three disks to allow for this parity information. When a disk fails, the system uses the parity information in those stripes in conjunction with the data on the other disks to re-create the data on the failed disk.
Disk striping writes data simultaneously across all physical disks in a RAID array. Each strip consists of consecutive data addresses that are mapped in fixed-size units to each physical disk in the array using a sequential pattern. For example, if the RAID array consists of four physical disks, the stripe writes data to physical disks one through four without having to repeat any of the physical disks.