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5x 20TB RAID-Z2 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 5x 20TB in RAID-Z2. Includes reserve planning for NAS and homelab arrays.

Capacity Snapshot

Raw Capacity

100.00 TB

Usable Capacity

54.00 TB

Fault Tolerance

2 drives

Efficiency

60.0%

Popular TrueNAS default for medium arrays; dual-parity with good safety margin. This scenario applies a 10% filesystem reserve.

Run Interactive Calculator →

Alternative Mode Comparison

Mode Usable Tolerance Efficiency
RAID 5 72.00 TB 1 drive 80.0%
RAID 6 54.00 TB 2 drives 60.0%
RAID 10 N/A N/A N/A
RAID-Z1 72.00 TB 1 drive 80.0%
RAID-Z2 54.00 TB 2 drives 60.0%

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: 5x 20TB RAID-Z1 NAS Calculator | Usable TB Next: 6x 4TB RAID 1 NAS Calculator | Usable TB →

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.

How many disk failures can RAID-Z2 tolerate in this setup?

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

How much effective storage does 5x 20TB RAID-Z2 provide?

This NAS planning scenario estimates 54.00 TB usable after a 10% reserve from 100.00 TB raw.

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.