Synology 6x 20TB RAID 10 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Synology NAS users using 6x 20TB in RAID 10.

Capacity Snapshot

Raw Capacity

120.00 TB

Usable Capacity

54.00 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.

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Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	90.00 TB	1 drive	83.3%
RAID 6	72.00 TB	2 drives	66.7%
RAID 10	54.00 TB	1 drive per mirror pair*	50.0%
RAID-Z1	90.00 TB	1 drive	83.3%
RAID-Z2	72.00 TB	2 drives	66.7%

Synology Planning Notes

Synology users usually optimize for predictable rebuild behavior and conservative free-space policies, especially when using large-capacity SHR/RAID pools for media and backup workloads.

• Keep spare bays in your growth plan so expansions do not force emergency migrations.
• Budget extra free space for snapshot retention and background indexing tasks.
• Prefer dual-parity style layouts for larger pools with long rebuild windows.

Brand / Region Glossary

SHR

Synology Hybrid RAID that improves flexibility when mixing drive sizes.

Btrfs Snapshots

Point-in-time snapshots used for rollback and data protection policies.

Storage Pool

Logical disk group where RAID layout is created before volumes are provisioned.

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 much real-world usable storage does 6x 20TB RAID 10 provide?

For Synology users, this NAS planning scenario estimates 54.00 TB usable after a 10% reserve from 120.00 TB raw.

How many disk failures can RAID 10 tolerate in this setup?

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

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.

Should I optimize this 6-drive plan for available space 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.