US 4x 20TB RAID-Z1 NAS Calculator

Estimate usable TB, parity, and fault tolerance for US homelab buyers using 4x 20TB in RAID-Z1.

Capacity Snapshot

Raw Capacity

80.00 TB

Usable Capacity

54.00 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	54.00 TB	1 drive	75.0%
RAID 6	36.00 TB	2 drives	50.0%
RAID 10	36.00 TB	1 drive per mirror pair*	50.0%
RAID-Z1	54.00 TB	1 drive	75.0%
RAID-Z2	36.00 TB	2 drives	50.0%

US Buyer Context

US buyers often evaluate frequent pricing swings and promo cycles. Capacity planning should account for staged purchases instead of one-time all-disk upgrades.

• Use parity layouts that remain valid during phased expansions.
• Compare total usable-per-dollar across multiple disk sizes, not only one SKU.

Brand / Region Glossary

Cost-per-Usable-TB

Planning metric that compares real usable capacity after reserve and parity.

Promo Window

Seasonal pricing period used for phased drive purchasing strategies.

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 much real-world usable storage does 4x 20TB RAID-Z1 provide?

For US homelab buyers, this NAS planning scenario estimates 54.00 TB usable after a 10% reserve from 80.00 TB raw.

Should I optimize this 4-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.

Is RAID-Z1 still viable with 20TB drives?

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

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.