What is RAID 6?

Do you know what is RAID 6? Here is the answer according to HP:

RAID 6 (ADG) is an extension of RAID 5 for implementation on arrays of four or more drives. The data and two sets of parity information are striped across all drives in the array. The additional set of parity improves the fault tolerance of the array but results in lower write performance. The two sets of parity information are stored in different locations across the drives in the array and occupy the equivalent capacity of two physical drives. RAID 6 protects against the simultaneous failure of two drives in the array.

I have also summarized the differences between different RAID levels.

RAID 0

• Function: Data is distributed across separate disk drives.
• Applications: Image Editing • Video Production • Pre-Press Applications
• Limitations: Highly vulnerable to failure. The entire array will fail if one drive fails.

RAID 1

• Function: Mirroring - Identical data stored on two drives, high fault tolerance, very good performance (higher read performance than RAID 0).
• Applications: Accounting • Payroll • Financial
• Limitations: 50% of capacity dedicated to fault protection. Doubles the number of drives required.

RAID 1+0

• Function: Implemented as striped, mirrored disks.
• Applications: Database applications requiring high performance and fault tolerance; sacrifices storage efficiency.

RAID 5

• Function: One set of parity data is distributed across all drives. Protects against the failure of any one drive in an array.
• Applications: Transaction processing • File and application servers • ERP • Internet and Intranet servers
• Limitations: Potentially risky for large arrays. Can only withstand the loss of one drive without total array failure. Low write performance (improved with battery-backed cache).

RAID 6

• Function: Two sets of parity data are distributed across all drives. Protects against the failure of two drives in an array. Provides higher fault tolerance than RAID 5.
• Applications: For 24x7 applications that require a higher level of fault tolerance than RAID 5.
• Limitations: Lower write performance than other RAID levels. Sequential and burst-write performance can be much improved with battery-backed cache.