RAID (Redundant Array of Independent Disks)

Tobo · ‎11.03.2025

RAID (Redundant Array of Independent Disks)

Definition

A RAID system (redundant array of independent disks) is used to organize multiple physical mass storage devices (usually hard disk drives or solid-state drives) into a logical drive. The goals are to obtain either greater fail-safety or greater data throughput over a single physical storage medium.

The most commonly used RAID levels are:

RAID 0: Striping - acceleration without redundancy.

RAID 0 offers increased transfer rates by dividing the hard disks involved into contiguous blocks of the same size (striping). This requires at least two mass storage devices. The increase in data throughput is based on the fact that the necessary hard disk accesses can be processed in parallel to a greater extent.

Advantage: Data processing can be significantly increased by parallel writing and reading.

Disadvantage: If one of the storage media fails due to a defect, the data from the other is also no longer usable because the partial information from the defective medium is missing.

RAID 0 is therefore only recommended in applications where fail-safety is of little importance.

RAID 1: Mirroring

RAID 1 is a group of usually two mass storage devices. A RAID 1 stores the same data on all hard disks (mirroring) and thus offers full redundancy. However, the total capacity of the array is at most as large as the smallest hard disk involved.

Advantage: If one of the mirrored mass storage devices fails, the other can continue to supply all data.

Disadvantage: Mirroring reduces the actual storage capacity.

RAID 5: Performance + Parity, Block-Level Striping with Distributed Parity Information

RAID 5 implements striping with block-level distributed parity information. To calculate the parity, a logical group is formed by the data blocks of the hard disks involved in the RAID array, which are each at the same address. Of all the data blocks in a group, one data block contains the parity data, while the other data blocks contain user data. The user data of RAID 5 groups is distributed among all hard disks as in RAID 0. The parity information is also distributed. RAID 5 requires at least three mass storage devices.

Advantage: RAID 5 offers both increased data throughput when reading data and redundancy at relatively low cost.

Disadvantages RAID 5 has slower write performance due to parity calculations. Long recovery times and data loss risk if a second drive fails. Requires a more complex controller compared to other RAID levels.

RAID 6: Disk Striping with Double Parity

RAID 6 improves data security compared to RAID 5 through two parity stripes that tolerate the failure of up to two drives in the array. The technology distributes parity data across multiple drives and optimizes I / O overlaps. For high-capacity drives with long reconstruction times, RAID 6 offers a significant reliability advantage. At least four drives are required.

Advantages: RAID 6 provides protection through a double parity structure during simultaneous drive failures. Storage capacity increases with the number of drives, while resource consumption remains lower compared to mirroring RAID levels.

Disadvantages: RAID 6 has lower performance than RAID 5, especially during simultaneous drive reconstruction. Implementation is cost-intensive due to additional parity drives and specialized controllers. RAID co-processors can optimize parity calculation and write performance.

RAID 10: Disk Mirroring and Striping

RAID 10, also known as RAID 1+0, combines disk mirroring and striping through mirroring followed by striping. This nested RAID technique offers an alternative redundancy strategy with lower fault tolerance. At least four drives are required.

Advantages: RAID 10 distributes data across multiple drives and uses parallel read / write heads for faster processing. The RAID-1 component ensures data protection, with mirror copies immediately taking over in case of failure.

Disadvantages: Drive failures in stripe sets impair failover performance. Four drives as a minimum requirement increase costs. Redundancy reduces usable storage capacity by 50%.

RAID 7: Non-Standard with Caching

RAID 7 represents a proprietary, non-standardized RAID level based on RAID 3 and RAID 4 concepts and extended by caching mechanisms. The technology was exclusively owned by the former Storage Computer Corp. and required specific hardware implementations.