FA-72053 / Error-correcting codes / Member archive

RAID-6 multiplies by g to the i instead of dividing · case 03

Rebuilt blocks are wrong except on disk 0.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Recover one missing data block of a RAID-6 stripe over GF(2^8) (0x11D). data has exactly one None (else None is returned). P = XOR of data; Q = sum of g^k * D_k with g = 2 and k the 0-based disk index. Use P when it is available; otherwise rebuild D_i = (Q + sum over present k of g^k D_k) * g^(-i); if neither is available return None.

Why this case matters

Dual-parity arrays rebuild a data disk from the Q syndrome when the P disk has also failed.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression [[220, 10, null], null, 95]	`102`	`236`	Failed

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