NAS planning example

5x 18TB RAID 1 NAS Calculator | Usable TB

Estimate usable TB, parity overhead, and fault tolerance for 5x 18TB in RAID 1. Includes reserve planning for NAS and homelab arrays.

Open calculator Open guide path

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

What this calculator can—and cannot—decide

The capacity model makes drive count, drive size, RAID layout, and reserve visible. It is a planning aid: it does not predict exact performance, rebuild duration, hardware compatibility, or the probability of data loss for a specific 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

90.00 TB

Usable Capacity

16.20 TB

Fault Tolerance

4 drives*

Efficiency

20.0%

Strong redundancy but low capacity efficiency. Great for small, critical datasets. This scenario applies a 10% filesystem reserve.

Run Interactive Calculator →

Alternative Mode Comparison

Mode	Usable	Tolerance	Efficiency
RAID 5	64.80 TB	1 drive	80.0%
RAID 6	48.60 TB	2 drives	60.0%
RAID 10	N/A	N/A	N/A
RAID-Z1	64.80 TB	1 drive	80.0%
RAID-Z2	48.60 TB	2 drives	60.0%

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

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

← Previous: 5x 16TB RAID-Z2 NAS Calculator | Usable TB Next: 5x 18TB RAID 5 NAS Calculator | Usable TB →

FAQ

How much real-world usable storage does 5x 18TB RAID 1 provide?

This NAS planning scenario estimates 16.20 TB usable after a 10% reserve from 90.00 TB raw.

How many disk failures can RAID 1 tolerate in this setup?

This setup can tolerate 4 drives*. 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.

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.