RAID Storage

Redundant arrays of independent disks (RAID) are used to overcome two bottlenecks associated with disk storage:

By using additional redundant disks we can increase both. The following are some typically identified RAID levels:

0: Nonredundant: Data is distributed across different disks to increase performance
1: Mirrored: A second disk set keeps a copy of the data (50% overhead)
0+1 (or 10): Striping and mirroring: Data is distributed across a second disk set to increase performance
2: Error correcting codes: Additional check disks (4:3, 10:4, 25:5) are used to provide redundancy with a smaller overhead (e.g. 57%, 71%, 83%)
3: Bit-interleaved parity: A single additional check disk is used to recover the data by distributing bits across all disks
4: block-interleaved parity: The check disk contains the parity on a block level: higher read throughput
5: block-interleaved distributed parity: Block parity is distributed across all disks: higher read and write throughput
6: higher redundancy: Like 5 with an additional check disk guarding against a second failure