NAS pSEO Landing
Estimate usable TB, parity overhead, and fault tolerance for 8x 4TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.
Raw Capacity
32.00 TB
Usable Capacity
21.60 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 | 25.20 TB | 1 drive | 87.5% |
| RAID 6 | 21.60 TB | 2 drives | 75.0% |
| RAID 10 | 14.40 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 25.20 TB | 1 drive | 87.5% |
| RAID-Z2 | 21.60 TB | 2 drives | 75.0% |
For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.
It can be practical, but larger drives increase rebuild windows. Validate parity choice and backup policy before committing to the final layout.
Keeping free space improves filesystem behavior for snapshots, metadata, and write performance. Full arrays often perform worse and rebuild more slowly.
This NAS planning scenario estimates 21.60 TB usable after a 10% reserve from 32.00 TB raw.