Unraid 8x 16TB RAID-Z2 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Unraid NAS users using 8x 16TB in RAID-Z2.

Capacity Snapshot

Raw Capacity

128.00 TB

Usable Capacity

86.40 TB

Fault Tolerance

2 drives

Efficiency

75.0%

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	100.80 TB	1 drive	87.5%
RAID 6	86.40 TB	2 drives	75.0%
RAID 10	57.60 TB	1 drive per mirror pair*	50.0%
RAID-Z1	100.80 TB	1 drive	87.5%
RAID-Z2	86.40 TB	2 drives	75.0%

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

Is RAID-Z2 still practical with 16TB drives?

It can be practical, but larger drives increase rebuild windows. Validate parity choice and backup policy before committing to the final layout.

Should I optimize this 8-drive plan for capacity 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.

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 8x 16TB RAID-Z2 provide?

For Unraid users, this NAS planning scenario estimates 86.40 TB usable after a 10% reserve from 128.00 TB raw.