Unraid 4x 16TB RAID-Z2 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Unraid NAS users using 4x 16TB in RAID-Z2.

Capacity Snapshot

Raw Capacity

64.00 TB

Usable Capacity

28.80 TB

Fault Tolerance

2 drives

Efficiency

50.0%

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

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Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	43.20 TB	1 drive	75.0%
RAID 6	28.80 TB	2 drives	50.0%
RAID 10	28.80 TB	1 drive per mirror pair*	50.0%
RAID-Z1	43.20 TB	1 drive	75.0%
RAID-Z2	28.80 TB	2 drives	50.0%

Unraid Planning Notes

Unraid users often optimize for incremental growth and flexible disk replacement, where parity planning and usable capacity targets evolve over time rather than all at once.

• Capacity plans should include phased drive upgrades, not only day-one layout.
• Use parity-protected growth steps to avoid risky bulk migrations.
• Track cache and parity pressure separately from archive data growth.

Brand / Region Glossary

Parity Disk

Dedicated parity disk(s) protecting data disks in the Unraid array model.

Cache Pool

Fast SSD/NVMe pool used for writes and application workloads.

Mover

Scheduled process that migrates data between cache and array tiers.

NAS Cluster Guides

NAS Hub RAID Level Compare RAID Capacity Matrix Planning Quick Sheet RAID Selector NAS FAQ

Related Long-Tail Calculators

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Sequential Long-Tail Navigation

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FAQ

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.

Should I optimize this 4-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.

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.