FA-72034 / Error-correcting codes / Member archive

RAID-5 parity rotates in the right-asymmetric direction · case 04

Rebuilt stripes return parity as data for most stripes.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

RAID-5 left-symmetric layout on n >= 3 disks: in stripe s the parity lives on disk n-1-(s mod n) and data chunk j lives on disk (parity + 1 + j) mod n. blocks lists the stripe per disk (ints; at most one None for a failed disk). A missing block is rebuilt by XOR; with no missing block the XOR of all blocks must be 0 or the result is "parity-mismatch". Return [data chunks in logical order, parity block].

Why this case matters

Array controllers rebuild degraded stripes and must map disks to logical chunks correctly.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression [[96, 103, null, 49], 3, 4]	`[[96, 103, 54], 49]`	`[[103, 54, 49], 96]`	Failed

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