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4x 10TB RAID-Z2 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 4x 10TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

40.00 TB

Usable Capacity

18.00 TB

Fault Tolerance

2 drives

Efficiency

50.0%

Popular TrueNAS default for medium arrays; dual-parity with good safety margin. This scenario applies a 10% filesystem reserve.

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Alternative Mode Comparison

Mode Usable Tolerance Efficiency
RAID 5 27.00 TB 1 drive 75.0%
RAID 6 18.00 TB 2 drives 50.0%
RAID 10 18.00 TB 1 drive per mirror pair* 50.0%
RAID-Z1 27.00 TB 1 drive 75.0%
RAID-Z2 18.00 TB 2 drives 50.0%

NAS Cluster Guides

NAS Hub RAID Level Compare RAID Capacity Matrix Planning Quick Sheet RAID Selector NAS FAQ

Related Long-Tail Calculators

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Sequential Long-Tail Navigation

← Previous: 4x 10TB RAID-Z1 NAS Calculator | Usable TB Next: 4x 12TB RAID 1 NAS Calculator | Usable TB →

FAQ

How much real-world usable storage does 4x 10TB RAID-Z2 provide?

This NAS planning scenario estimates 18.00 TB usable after a 10% reserve from 40.00 TB raw.

Should I optimize this 4-drive plan for capacity or resiliency first?

For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.

How many disk failures can RAID-Z2 tolerate in this setup?

This setup can tolerate 2 drives. Real-world survivability depends on mirror placement, rebuild stress, and drive health.

Can this calculator replace real-world benchmark and rebuild testing?

No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.