RAID is a data storage technology that combines multiple physical disk drives into one or more logical units for data redundancy, performance improvement, or both. RAID stands for either Redundant Array of Independent Disks or Redundant Array of Inexpensive Disks, depending on the type of drives used.
There are different RAID levels, each optimized for a specific situation. These are not standardized by an industry group or standardization committee, so some manufacturers may use different names or implementations for the same RAID level.
Some of the most popular RAID levels are:
• RAID 0: Striping: In this level, data are split up into blocks that get written across all the drives in the array. This offers superior I/O performance, but no fault tolerance. If one drive fails, all data in the RAID 0 array are lost. This level is ideal for non-critical storage of data that have to be read/written at a high speed, such as on an image retouching or video editing station.
• RAID 1: Mirroring: In this level, data are written identically to two or more drives, creating a mirror image of each other. This offers high data availability and fault tolerance, but reduces the storage capacity by half. If one drive fails, the other drive(s) can continue to serve the data. This level is ideal for critical storage of data that need maximum protection against drive failures, such as on a server or a personal computer.
• RAID 5: Striping with parity: In this level, data are striped across three or more drives, and a parity block is written to each drive. The parity block contains information that can be used to reconstruct the data in case of a drive failure. This offers a balance between performance, storage capacity, and fault tolerance. If one drive fails, the data can be recovered from the remaining drives using the parity blocks. This level is ideal for storage of data that need moderate protection against drive failures, such as on a file server or a database server.
• RAID 6: Striping with double parity: In this level, data are striped across four or more drives, and two parity blocks are written to each drive. The parity blocks use different algorithms to create more redundancy than RAID 5. This offers a higher level of fault tolerance than RAID 5, but also a higher performance penalty. If two drives fail, the data can still be recovered from the remaining drives using the parity blocks. This level is ideal for storage of data that need high protection against drive failures, such as on a backup server or a mission-critical server.
• RAID 10: Combining mirroring and striping: In this level, data are striped across two or more mirrored sets of drives. This combines the advantages of RAID 0 and RAID 1, offering high performance and high fault tolerance. If one drive from each mirrored set fails, the data can still be accessed from the remaining drives. This level is ideal for storage of data that need both high performance and high protection against drive failures, such as on a high-end server or a workstation.