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5x 8TB RAID 5 NAS Calculator | Usable TB

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

Capacity Snapshot

Raw Capacity

40.00 TB

Usable Capacity

28.80 TB

Fault Tolerance

1 drive

Efficiency

80.0%

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	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

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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

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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.

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

This NAS planning scenario estimates 28.80 TB usable after a 10% reserve from 40.00 TB raw.

Can this calculator replace real-world benchmark and rebuild testing?

No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.

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.