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8x 18TB RAID 5 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 8x 18TB in RAID 5. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

144.00 TB

Usable Capacity

113.40 TB

Fault Tolerance

1 drive

Efficiency

87.5%

Balanced capacity and redundancy, but rebuild stress can be high on large disks. This scenario applies a 10% filesystem reserve.

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Alternative Mode Comparison

Mode Usable Tolerance Efficiency
RAID 5 113.40 TB 1 drive 87.5%
RAID 6 97.20 TB 2 drives 75.0%
RAID 10 64.80 TB 1 drive per mirror pair* 50.0%
RAID-Z1 113.40 TB 1 drive 87.5%
RAID-Z2 97.20 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 5 tolerate in this setup?

This setup can tolerate 1 drive. 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 18TB RAID 5 provide?

This NAS planning scenario estimates 113.40 TB usable after a 10% reserve from 144.00 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.