How this calculator works
Use equal-capacity drives or the smallest participating drive size. RAID 1 here mirrors all listed drives into one copy set; RAID 10 uses two-drive mirrors. Filesystem metadata, hot spares and controller reservations are excluded. RAID is not a backup.
The formula
Usable drives: RAID 0 = N; RAID 1 = 1; RAID 5 = N−1; RAID 6 = N−2; RAID 10 = N/2. Multiply by drive capacity.A quick example
Four 4 TB drives in RAID 5 have 16 TB raw capacity, 12 TB nominal usable capacity and 4 TB used for parity.
How to use this calculator
- Choose the settings that match your scenario, using the units shown beside each field.
- Enter raid level, number of equal-capacity drives, capacity per drive (tb, decimal).
- Calculate, then review the method and assumptions alongside the results.
A few common questions
Why does RAID 10 require an even drive count?
This model uses striped two-drive mirror pairs, requiring at least two pairs.
Will my operating system display exactly this capacity?
Usually not. Binary display units and filesystem/controller overhead change the reported usable number.
Reference: Dell: RAID levels and specifications