RAID Calculator
Calculate usable capacity and fault tolerance for RAID 0, 1, 5, 6 and 10.
About the RAID Calculator
RAID 0 stripes for speed with no redundancy. RAID 1 mirrors. RAID 5 spends one drive's worth of capacity on parity and survives one failure; RAID 6 spends two and survives two. RAID 10 mirrors pairs and stripes across them. RAID isn't a backup: deletion, ransomware and controller faults affect all copies.
The formula
RAID 5 = (n − 1) × size; RAID 6 = (n − 2) × size; RAID 10 = n ÷ 2 × size
Worked example
Example: Usable capacity = 27 TB
- Inputs: RAID level: RAID 5; Number of drives: 4; Drive size: 9 TB.
- Formula: RAID 5 = (n − 1) × size; RAID 6 = (n − 2) × size; RAID 10 = n ÷ 2 × size
- Result: Usable capacity = 27 TB
Questions people ask
Why is RAID 5 discouraged for big drives?
Rebuilds take long and another failure or read error during rebuild loses data.
Why does my OS show less?
Drives use decimal TB; operating systems often show binary TiB.