RAID LEVEL 6: Independent Data Disks with Two Independent Parity Schemes

Click on the diagram to see Raid 6 in action

Two independent parity computations must be used in order to provide protection against double disk failure. Two different algorithms are employed to achieve this purpose.

RAID Level 6 requires a minimum of 4 drives to implement

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Characteristics & Advantages

  • RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity)
  • Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures
  • RAID 6 protects against multiple bad block failures while non-degraded
  • RAID 6 protects against a single bad block failure while operating in a degraded mode
  • Perfect solution for mission critical applications

Disadvantages

  • More complex controller design
  • Controller overhead to compute parity addresses is extremely high
  • Write performance can be brought on par with RAID Level 5 by using a custom ASIC for computing Reed-Solomon parity
  • Requires N+2 drives to implement because of dual parity scheme

Recommended Applications

  • File and Application servers
  • Database servers
  • Web and E-mail servers
  • Intranet servers
  • Excellent fault-tolerance with the lowest overhead
 
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