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8x 18TB RAID-Z1 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 8x 18TB in RAID-Z1. 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%

ZFS single-parity equivalent of RAID 5; common for smaller homelab pools. 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

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 available space?

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

How many disk failures can RAID-Z1 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 8x 18TB RAID-Z1 provide?

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