Understanding RAID level-6

RAID level-6 is similar to RAID level-5 but with two sets of parity information instead of one. RAID level-6 stripes blocks of data and parity across all drives in the array like RAID level-5, but adds a second set of parity information for each block of data.

When you assign RAID level-6 to an array, the capacity of the array is reduced for data-parity storage (the exact amount depends on the size of the drives in the array). The second set of parity information is added to improve fault tolerance. RAID level-6 can handle two simultaneous drive failures, where other single RAID levels can handle, at most, only one.

RAID level-6 requires a minimum of four drives and supports a maximum of 16 drives. The maximum stripe-unit size depends on the number of drives in the array.

The following illustration is an example of a RAID level-6 logical drive.

RAID level-6 example

Start with six physical drives.
Create a logical drive using four physical drives, leaving two for hot spare drives.

 

The data is striped across the drives, creating blocks in the logical drive. The storage of the data parity (denoted by * and **) is striped, and it shifts from drive to drive as it does in RAID level-5.
If a physical drive fails in the array, the logical drive is degraded but remains fault tolerant.
If a second physical drive fails in the array, the data from the failed drives are reconstructed onto the hot-spare drives, and the data for the logical drive return to the original striping scheme.

RAID level-6 offers the following advantages and disadvantages.
Advantages Disadvantages
  • 100% data protection
  • Extremely high data fault tolerance
  • Can sustain two simultaneous drive failures
  • Good solution for mission critical applications

  • Lower performance than RAID level-5 because of two parity drives
  • Not supported on all controllers

 

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