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8x 20TB RAID 1 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 8x 20TB in RAID 1. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

160.00 TB

Usable Capacity

18.00 TB

Fault Tolerance

7 drives*

Efficiency

12.5%

Strong redundancy but low capacity efficiency. Great for small, critical datasets. 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

Related Long-Tail Calculators

2x 4TB RAID 1 2x 6TB RAID 1 2x 8TB RAID 1 2x 10TB RAID 1 2x 12TB RAID 1 2x 14TB RAID 1 2x 16TB RAID 1 2x 18TB RAID 1 2x 20TB RAID 1 3x 4TB RAID 1 3x 4TB RAID 5 3x 4TB RAID-Z1 3x 6TB RAID 1 3x 6TB RAID 5 3x 6TB RAID-Z1 3x 8TB RAID 1

Sequential Long-Tail Navigation

← Previous: 8x 18TB RAID-Z2 NAS Calculator | Usable TB Next: 8x 20TB RAID 5 NAS Calculator | Usable TB →

FAQ

How many disk failures can RAID 1 tolerate in this setup?

This setup can tolerate 7 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 20TB RAID 1 provide?

This NAS planning scenario estimates 18.00 TB usable after a 10% reserve from 160.00 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.