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8x 20TB RAID 6 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 8x 20TB in RAID 6. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

160.00 TB

Usable Capacity

108.00 TB

Fault Tolerance

2 drives

Efficiency

75.0%

Safer for larger arrays with dual parity, at the cost of one extra parity disk. This scenario applies a 10% filesystem reserve.

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Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	126.00 TB	1 drive	87.5%
RAID 6	108.00 TB	2 drives	75.0%
RAID 10	72.00 TB	1 drive per mirror pair*	50.0%
RAID-Z1	126.00 TB	1 drive	87.5%
RAID-Z2	108.00 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 much real-world usable storage does 8x 20TB RAID 6 provide?

This NAS planning scenario estimates 108.00 TB usable after a 10% reserve from 160.00 TB raw.

Is RAID 6 still worth deploying with 20TB drives?

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

How many disk failures can RAID 6 tolerate in this setup?

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

Why include a 10% reserve when planning NAS available space?

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