What is RAID?

RAID (redundant array of independent disks) is a storage technology that combines multiple disk components into a logical unit. Different RAID levels define different configurations to employ striping, mirroring, or parity.

RAID levels

RAID 0 - block-striped volume

• splits data across 2 or more disks
• no data redundancy
• no parity
• used to increase performance
• used to create a large logical disk out of 2 or more physical ones
• size = n x min(all drive sizes)

RAID 1 - mirror

• exact copy of data on 2 disks
• size = n x min(all drive sizes)
• does not provide protection against data corruption due to viruses, accidental file changes or deletions, or any other data-specific changes
• speed = n * disk speed
• use independent disk controllers to increase speed

RAID 2 - bit striped volume

• stripes data at the bit level; uses hamming code for error correction
• no commercial applications of RAID 2 today

RAID 3

• byte-level striping with a dedicated parity disk
• cannot serve multiple requests simultaneously
• not commonly used

RAID 4

• block-level striping with a dedicated parity disk
• not commonly used

RAID 5

• block-level striping with parity data

RAID 6

• block-level striping with two parity blocks
• penalty on write operations

RAID 10 - mirror stripes

• top level RAID 0 array composed of 2 or more RAID 1 arrays

RAID 0+1 - striped mirrors

• top level RAID 1 mirror composed of two or more RAID 0 strip sets