Plan a RAID array's capacity
Five drives do not mean five drives of storage — RAID levels trade capacity for survivability.
Tools used in this guide
The job
RAID 0 stripes for speed and dies with any disk; RAID 5 survives one; RAID 6 two; RAID 10 halves capacity for mirrored speed. The question is how much usable space your drive count buys.
Level, count, size
Pick the level, enter drive count and per-drive size. Output is usable capacity, the number of drives' worth spent on redundancy, and tolerated failures.
Worked example
6 × 4 TB: RAID 0 → 24 TB (0 safe), RAID 5 → 20 TB (1 safe), RAID 6 → 16 TB (2 safe), RAID 10 → 12 TB (1, sometimes more).
Where it stops
Identical drives, decimal TB, no filesystem or hot-spare overhead — real usable space lands a few percent lower. RAID is not backup; a second copy still matters.