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8x 12TB RAID-Z2 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 8x 12TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

96.00 TB

Usable Capacity

64.80 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.

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Alternative Mode Comparison

Mode Usable Tolerance Efficiency
RAID 5 75.60 TB 1 drive 87.5%
RAID 6 64.80 TB 2 drives 75.0%
RAID 10 43.20 TB 1 drive per mirror pair* 50.0%
RAID-Z1 75.60 TB 1 drive 87.5%
RAID-Z2 64.80 TB 2 drives 75.0%

NAS Cluster Guides

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

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Sequential Long-Tail Navigation

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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.

Should I optimize this 8-drive plan for storage headroom 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 much real-world usable storage does 8x 12TB RAID-Z2 provide?

This NAS planning scenario estimates 64.80 TB usable after a 10% reserve from 96.00 TB raw.

Why include a 10% reserve when planning NAS capacity?

Keeping free space improves filesystem behavior for snapshots, metadata, and write performance. Full arrays often perform worse and rebuild more slowly.