RAID 6 Recovery

RAID 6 parameters

RAID 6 layout utilizes two different parity functions which helps a RAID 6 array survive up to double disk failure. Despite of the fact that RAID6 is perceived to be more reliable than a RAID 5, the probability of a controller failure is the same. So if your RAID6 fails, this will most likely be due to a controller failure. To recover a RAID6 from a controller failure, you need to know or recover the following parameters:

  • number of member disks,
  • disk order and which disk was the first in the array,
  • block size,
  • start offset on the member disks,
  • positions of each parity function,
  • rotation of parity functions,
  • algorithm used to calculate the second parity function,
  • pattern of parity functions.

You should know all these parameters to reconstuct RAID 6 successfully. Our software ReclaiMe Free RAID Recovery (download) can recover RAID6 configuration automatically. See the step-by-step RAID Recovery instructions.

RAID 6 variations

RAID 6 is significantly more complex than RAID 5.

  • The first parity function (XOR, denoted as P on the diagrams) naturally comes from RAID5. However, there is no widely accepted standard for the second parity function (Q). Typically, a Reed-Solomon code or some variation thereof is used.
  • Reed-Solomon code depends on the order in which input is provided. This produces four more variations: left-to-right or right-to-left and if P or Q is calculated first.
  • There are several variations of layout accomodating two parity functions.

RAID6 P-bottom and P-top layouts
RAID 6 WidePace (Promise hardware setup)

Missing disk limitations

Although RAID 6 should be recoverable with one or two disks missing, the implementation of ReclaiMe Free RAID Recovery cannot work with RAID6 having missing disks.

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