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12x 20TB RAID-Z1 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 12x 20TB in RAID-Z1. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

240.00 TB

Usable Capacity

198.00 TB

Fault Tolerance

1 drive

Efficiency

91.7%

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 5 198.00 TB 1 drive 91.7%
RAID 6 180.00 TB 2 drives 83.3%
RAID 10 108.00 TB 1 drive per mirror pair* 50.0%
RAID-Z1 198.00 TB 1 drive 91.7%
RAID-Z2 180.00 TB 2 drives 83.3%

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

← Previous: 12x 20TB RAID 10 NAS Calculator | Usable TB Next: 12x 20TB RAID-Z2 NAS Calculator | Usable TB →

FAQ

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.

Why include a 10% reserve when planning NAS storage headroom?

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

How much real-world usable storage does 12x 20TB RAID-Z1 provide?

This NAS planning scenario estimates 198.00 TB usable after a 10% reserve from 240.00 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.