NAS pSEO Landing
Estimate usable TB, parity overhead, and fault tolerance for 12x 12TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.
Raw Capacity
144.00 TB
Usable Capacity
108.00 TB
Fault Tolerance
2 drives
Efficiency
83.3%
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 | 118.80 TB | 1 drive | 91.7% |
| RAID 6 | 108.00 TB | 2 drives | 83.3% |
| RAID 10 | 64.80 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 118.80 TB | 1 drive | 91.7% |
| RAID-Z2 | 108.00 TB | 2 drives | 83.3% |
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.
For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.
It can be practical, but larger drives increase rebuild windows. Validate parity choice and backup policy before committing to the final layout.