Synology 4x 12TB RAID-Z1 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Synology NAS users using 4x 12TB in RAID-Z1.

Capacity Snapshot

Raw Capacity

48.00 TB

Usable Capacity

32.40 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	32.40 TB	1 drive	75.0%
RAID 6	21.60 TB	2 drives	50.0%
RAID 10	21.60 TB	1 drive per mirror pair*	50.0%
RAID-Z1	32.40 TB	1 drive	75.0%
RAID-Z2	21.60 TB	2 drives	50.0%

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 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.

Is RAID-Z1 still viable with 12TB drives?

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

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.

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.