RAID stands for Redundant Array of Inexpensive (Independent) Disks.

On most situations you will be using one of the following four levels of RAIDs.

  • RAID 0
  • RAID 1
  • RAID 2
  • RAID 3
  • RAID 4
  • RAID 5
  • RAID 6
  • RAID 10 (also known as RAID 1+0)

This article explains the main difference between these raid levels along with an easy to understand diagram.

In all the diagrams mentioned below:

  • A, B, C, D, E and F – represents blocks
  • p1, p2, and p3 – represents parity

RAID LEVEL 0

Following are the key points to remember for RAID level 0.

  • Minimum 2 disks.
  • Excellent performance ( as blocks are striped ).
  • No redundancy ( no mirror, no parity ).
  • Don’t use this for any critical system.

RAID LEVEL 1

Following are the key points to remember for RAID level 1.

  • Minimum 2 disks.
  • Good performance ( no striping. no parity ).
  • Excellent redundancy ( as blocks are mirrored ).

Random read performance of a RAID 1 array may equal up to the sum of each member's performance, while the write performance remains at the level of a single disk.

RAID LEVEL 2

Following are the key points to remember for RAID level 2.

  • Minimum 3 disks.
  • Excellent sequential performance(bit level stripe)
  • Good redundancy(bit level stripe, one parity)
  • Hamming-code parity is calculated across corresponding bits and stored on at least one parity drive.

This level is of historical significance only; although it was used on some early machines (for example, the Thinking Machines CM-2), as of 2014 it is not used by any of the commercially available systems

RAID LEVEL 3

Following are the key points to remember for RAID level 3.

  • Minimum 3 disks.
  • Excellent sequencial performance ( as bit striped ).
  • Good redundancy ( one parity disk ).
  • Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.

RAID 3 was usually implemented in hardware, and the performance issues were addressed by using large disk caches.

RAID LEVEL 4

Following are the key points to remember for RAID level 4.

  • Minimum 3 disks.
  • Good performance ( as blocks are striped ).
  • Good redundancy ( one parity disk ).

RAID 4 provides good performance of random reads, while the performance of random writes is low due to the need to write all parity data to a single disk.

RAID LEVEL 5


Following are the key points to remember for RAID level 5.

  • Minimum 3 disks.
  • Good performance ( as blocks are striped ).
  • Good redundancy ( distributed parity ).
  • Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.

In comparison to RAID 4, RAID 5's distributed parity evens out the stress of a dedicated parity disk among all RAID members. Additionally, read performance is increased since all RAID members participate in serving of the read requests.

RAID LEVEL 6

Following are the key points to remember for RAID level 6.

  • Minimum 4 disks.
  • Good performance ( as blocks are striped ).
  • Good redundancy ( 2 parity disks ).
  • Best cost effective option providing both performance and redundancy.

RAID 6 does not have a performance penalty for read operations, but it does have a performance penalty on write operations because of the overhead associated with parity calculations. Performance varies greatly depending on how RAID 6 is implemented in the manufacturer's storage architecture—in software, firmware, or by using firmware and specialized ASICs for intensive parity calculations. It can be as fast as a RAID 5 system with one fewer drive (same number of data drives.

RAID LEVEL 10

 

Following are the key points to remember for RAID level 10.

  • Minimum 4 disks.
  • This is also called as “stripe of mirrors”
  • Excellent redundancy ( as blocks are mirrored )
  • Excellent performance ( as blocks are striped )
  • If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).

More detail  see Standard RAID levels