Unraid 4x 8TB RAID-Z1 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Unraid NAS users using 4x 8TB in RAID-Z1.

Capacity Snapshot

Raw Capacity

32.00 TB

Usable Capacity

21.60 TB

Fault Tolerance

1 drive

Efficiency

75.0%

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	21.60 TB	1 drive	75.0%
RAID 6	14.40 TB	2 drives	50.0%
RAID 10	14.40 TB	1 drive per mirror pair*	50.0%
RAID-Z1	21.60 TB	1 drive	75.0%
RAID-Z2	14.40 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

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

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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.

How much usable storage does 4x 8TB RAID-Z1 provide?

For Unraid users, this NAS planning scenario estimates 21.60 TB usable after a 10% reserve from 32.00 TB raw.

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.

Is RAID-Z1 still worth deploying with 8TB drives?

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