NAS / RAID Capacity Calculator
Pick a layout, enter your drives, and see usable capacity, how many drives can fail, and storage efficiency — instantly, in your browser.
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Usable capacity
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Drives can fail
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Efficiency
Building the array? Start with the right drives.
Use CMR NAS drives (never SMR) for RAID/ZFS, and the right NAS to run it. New to all this? The Homelab Starter Blueprint walks you through planning storage end-to-end.
See the best NAS drives →How RAID capacity works
- RAID 0 — all space usable, zero redundancy (one drive dies, everything's gone). Speed only.
- RAID 1 — mirror; usable = one drive, survives all-but-one failing.
- RAID 5 / RAIDZ1 — usable = (drives − 1); survives 1 failure. Needs 3+ drives.
- RAID 6 / RAIDZ2 — usable = (drives − 2); survives 2 failures. Best for large drives. Needs 4+.
- RAIDZ3 — usable = (drives − 3); survives 3. Needs 5+.
- RAID 10 — usable = half; fast + resilient (survives 1 per mirror). Needs an even count, 4+.
RAID is not a backup. It protects against drive failure — not deletion, ransomware, or disaster. Always pair it with the 3-2-1 backup rule and a UPS.