EU 4x 20TB RAID 10 NAS Calculator

Estimate usable TB, parity, and fault tolerance for EU homelab buyers using 4x 20TB in RAID 10.

Capacity Snapshot

Raw Capacity

80.00 TB

Usable Capacity

36.00 TB

Fault Tolerance

1 drive per mirror pair*

Efficiency

50.0%

Excellent random I/O and rebuild behavior; capacity is typically 50% of raw. This scenario applies a 10% filesystem reserve.

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%

EU deployments often place additional emphasis on energy efficiency and predictable lifecycle upgrades, especially for always-on NAS fleets.

• Choose a layout that minimizes emergency rebuild risk under continuous operation.
• Prefer capacity plans that survive one upgrade cycle without pool redesign.

Capacity and reliability strategy across multiple hardware refresh cycles.

Intentional free-space margin to protect performance and snapshot behavior.

For EU homelab buyers, this NAS planning scenario estimates 36.00 TB usable after a 10% reserve from 80.00 TB raw.

No. Use this page for pre-purchase sizing, then validate with workload benchmarks, SMART health policy, and a tested restore plan.

For long-lived NAS pools, resiliency first is usually safer. Capacity can be expanded later, while a risky parity choice can force migration sooner.

This setup can tolerate 1 drive per mirror pair*. Real-world survivability depends on mirror placement, rebuild stress, and drive health.