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5x 8TB RAID-Z2 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 5x 8TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

40.00 TB

Usable Capacity

21.60 TB

Fault Tolerance

2 drives

Efficiency

60.0%

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 28.80 TB 1 drive 80.0%
RAID 6 21.60 TB 2 drives 60.0%
RAID 10 N/A N/A N/A
RAID-Z1 28.80 TB 1 drive 80.0%
RAID-Z2 21.60 TB 2 drives 60.0%

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: 5x 8TB RAID-Z1 NAS Calculator | Usable TB Next: 5x 10TB RAID 1 NAS Calculator | Usable TB →

FAQ

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.

How much usable storage does 5x 8TB RAID-Z2 provide?

This NAS planning scenario estimates 21.60 TB usable after a 10% reserve from 40.00 TB raw.

Should I optimize this 5-drive plan for available space 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.

Is RAID-Z2 still worth deploying with 8TB drives?

It can be practical, but larger drives increase rebuild windows. Validate parity choice and backup policy before committing to the final layout.