Synology 4x 12TB RAID 5 NAS Calculator

Estimate usable TB, parity, and fault tolerance for Synology NAS users using 4x 12TB in RAID 5.

Planning route

Answer the capacity question, then validate the purchase path

Use this worked example as a numeric starting point, then validate the RAID choice, capacity reserve, hardware plan, and backup path.

Decision aid RAID level selector Reference Capacity matrix

Editorial method

Turn the result into a storage brief

The capacity model makes drive count, drive size, RAID layout, and reserve visible. Use the resulting brief to check exact performance, rebuild duration, hardware compatibility, and the recovery plan for the chosen system.

Last reviewed: July 10, 2026. Product links remain neutral category searches until a partner relationship and page-level disclosure are in place.

OpenZFS checksums and scrubs Background on checksum verification, scrubs, and repair in suitably redundant ZFS pools. Read primary source ↗ TrueNAS data protection Official overview of scrubs, S.M.A.R.T. tests, snapshots, replication, and backup tasks. Read primary source ↗ CISA ransomware guidance Why recoverable, regularly tested backups should be separate from array redundancy. Read primary source ↗

Capacity Snapshot

Raw Capacity

48.00 TB

Usable Capacity

32.40 TB

Fault Tolerance

1 drive

Efficiency

75.0%

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	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 navigation

Move through the storage decision path

All apps

NAS Hub Calculator and buying path Learning Center 8-step guide path RAID Comparison Mode-by-mode matrix RAID Selector Choose by priority Capacity Matrix Citation-ready reference NAS FAQ Planning answers

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Sequential long-tail navigation

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FAQ

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.

How much usable storage does 4x 12TB RAID 5 provide?

For Synology users, this NAS planning scenario estimates 32.40 TB usable after a 10% reserve from 48.00 TB raw.

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.

Is RAID 5 still worth deploying 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.