Unraid (2 parity)
Unraid (2 parity)
Double-parity Unraid. Drive isolation + 2-failure tolerance. The Unraid choice for 5+ drives, 12 TB+ drives, or critical media you want to keep.
How it works
Same independent-filesystem model as Unraid 1P, but with two parity drives instead of one. Tolerates 2 simultaneous data drive failures. The second parity can also fill in for a URE during rebuild, so big-drive Unraid arrays stay rebuildable.
Formula: sum(data) — 2 parity drives
Pros / Cons
Pros
- Drive isolation + double parity
- Mixed sizes + 2-failure tolerance
- Tolerates a URE during rebuild
- Best for 5+ drive Unraid pools
- Same simple recovery model as 1P
Cons
- Loses 2 drives of capacity
- Paid license
- Two parity drives must each be ≥ largest data drive
- Parity-write penalty still applies
When to use
Unraid arrays with 5+ drives, 12 TB+ drives, or media collections you can't easily re-create.
When NOT to use
Tiny pools (2-3 drives, ≤ 8 TB) — 1 parity is fine and gives you 1 more drive of capacity.
Rebuild math example
8 × 8 TB Unraid 2P (2 parity + 6 data). Failed data drive: reads remaining 7 drives × 8 TB = 56 TB at 70 MB/s ≈ 110 hours. Second parity covers a URE during rebuild, so the rebuild is far more survivable.