RAID Calculator
Usable capacity and fault tolerance for RAID 0, 1, 5, 6 and 10.
How to use this tool
Enter the number of drives and the size of each drive. The calculator shows usable capacity, parity overhead and how many drive failures each level survives. RAID is availability, not backup.
Worked example
8 × 4 TB in RAID 6 = (8 − 2) × 4 = 24 TB usable and survives any two drive failures. RAID 5 would give 28 TB but survives only one.
Frequently asked questions
Is RAID a backup?
No. RAID keeps the system running through a drive failure; it does not protect against deletion, ransomware or controller failure.
RAID 5 or RAID 6 for NVR?
RAID 6 for large drives: rebuild times are long and a second failure during rebuild is a real risk.
Why does RAID 10 need an even number of drives?
It stripes across mirrored pairs, so drives must come in pairs.