NAS pSEO Landing
Estimate usable TB, parity overhead, and fault tolerance for 10x 18TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.
Raw Capacity
180.00 TB
Usable Capacity
129.60 TB
Fault Tolerance
2 drives
Efficiency
80.0%
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 | 145.80 TB | 1 drive | 90.0% |
| RAID 6 | 129.60 TB | 2 drives | 80.0% |
| RAID 10 | 81.00 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 145.80 TB | 1 drive | 90.0% |
| RAID-Z2 | 129.60 TB | 2 drives | 80.0% |
Keeping free space improves filesystem behavior for snapshots, metadata, and write performance. Full arrays often perform worse and rebuild more slowly.
For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.
This NAS planning scenario estimates 129.60 TB usable after a 10% reserve from 180.00 TB raw.
This setup can tolerate 2 drives. Real-world survivability depends on mirror placement, rebuild stress, and drive health.