NAS pSEO Landing
Brand Focus · TrueNAS
Estimate usable capacity, fault tolerance, and efficiency for TrueNAS NAS users using 4x 8TB in RAID 5.
Raw Capacity
32.00 TB
Usable Capacity
21.60 TB
Fault Tolerance
1 drive
Efficiency
75.0%
Balanced capacity and redundancy, but rebuild stress can be high on large disks. This scenario applies a 10% filesystem reserve.
Run Interactive Calculator →| Mode | Usable | Tolerance | Efficiency |
|---|---|---|---|
| RAID 5 | 21.60 TB | 1 drive | 75.0% |
| RAID 6 | 14.40 TB | 2 drives | 50.0% |
| RAID 10 | 14.40 TB | 1 drive per mirror pair* | 50.0% |
| RAID-Z1 | 21.60 TB | 1 drive | 75.0% |
| RAID-Z2 | 14.40 TB | 2 drives | 50.0% |
TrueNAS and ZFS planners usually care about parity width, scrub cadence, and healthy operating headroom. Capacity is only one part of pool durability.
A virtual device group in ZFS; multiple vdevs form a storage pool.
Background integrity scan that verifies checksums and repairs parity mismatches.
ZFS feature set and planning topic for growing parity groups safely.
This setup can tolerate 1 drive. 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.
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.