NAS pSEO Landing
Estimate usable TB, parity overhead, and fault tolerance for 4x 20TB in RAID 6. Includes reserve planning for NAS and homelab arrays.
Raw Capacity
80.00 TB
Usable Capacity
36.00 TB
Fault Tolerance
2 drives
Efficiency
50.0%
Safer for larger arrays with dual parity, at the cost of one extra parity disk. This scenario applies a 10% filesystem reserve.
Run Interactive Calculator →| Mode | Usable | Tolerance | Efficiency |
|---|---|---|---|
| RAID 5 | 54.00 TB | 1 drive | 75.0% |
| RAID 6 | 36.00 TB | 2 drives | 50.0% |
| RAID 10 | 36.00 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 54.00 TB | 1 drive | 75.0% |
| RAID-Z2 | 36.00 TB | 2 drives | 50.0% |
For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.
Keeping free space improves filesystem behavior for snapshots, metadata, and write performance. Full arrays often perform worse and rebuild more slowly.
No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.
This setup can tolerate 2 drives. Real-world survivability depends on mirror placement, rebuild stress, and drive health.