NAS pSEO Landing
Estimate usable TB, parity overhead, and fault tolerance for 8x 20TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.
Raw Capacity
160.00 TB
Usable Capacity
108.00 TB
Fault Tolerance
2 drives
Efficiency
75.0%
Popular TrueNAS default for medium arrays; dual-parity with good safety margin. This scenario applies a 10% filesystem reserve.
Run Interactive Calculator →| Mode | Usable | Tolerance | Efficiency |
|---|---|---|---|
| RAID 5 | 126.00 TB | 1 drive | 87.5% |
| RAID 6 | 108.00 TB | 2 drives | 75.0% |
| RAID 10 | 72.00 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 126.00 TB | 1 drive | 87.5% |
| RAID-Z2 | 108.00 TB | 2 drives | 75.0% |
No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.
Keeping free space improves filesystem behavior for snapshots, metadata, and write performance. Full arrays often perform worse and rebuild more slowly.
This setup can tolerate 2 drives. Real-world survivability depends on mirror placement, rebuild stress, and drive health.
It can be practical, but larger drives increase rebuild windows. Validate parity choice and backup policy before committing to the final layout.