Synology 8x 20TB RAID 5 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Synology NAS users using 8x 20TB in RAID 5.

Capacity Snapshot

Raw Capacity

160.00 TB

Usable Capacity

126.00 TB

Fault Tolerance

1 drive

Efficiency

87.5%

Balanced capacity and redundancy, but rebuild stress can be high on large disks. This scenario applies a 10% filesystem reserve.

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Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	126.00 TB	1 drive	87.5%
RAID 6	108.00 TB	2 drives	75.0%
RAID 10	72.00 TB	1 drive per mirror pair*	50.0%
RAID-Z1	126.00 TB	1 drive	87.5%
RAID-Z2	108.00 TB	2 drives	75.0%

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

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

Is RAID 5 still practical 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.

How many disk failures can RAID 5 tolerate in this setup?

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

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.