💾 RAID Calculator
Estimate the usable storage capacity and fault tolerance of a RAID array from the number of drives, drive size, and RAID level.
What this calculator does
RAID (Redundant Array of Independent Disks) combines multiple physical drives into one logical volume, trading off raw storage space for performance, redundancy, or both. This calculator estimates the usable capacity you actually get to store data on, after the overhead required by each RAID level’s redundancy scheme.
How the math works
- RAID 0 stripes data with no redundancy: usable capacity equals the sum of all drives (n × size), but a single drive failure loses all data.
- RAID 1 mirrors data across drives: usable capacity equals one drive’s size, tolerating one drive failure.
- RAID 5 uses one drive’s worth of capacity for parity: usable capacity is (n − 1) × size, requiring at least 3 drives and tolerating one failure.
- RAID 6 uses two drives’ worth for parity: usable capacity is (n − 2) × size, requiring at least 4 drives and tolerating two failures.
- RAID 10 mirrors pairs of drives and then stripes across the pairs: usable capacity is (n / 2) × size, requiring an even number of at least 4 drives.
Enter the number of drives, the size of each drive, and the RAID level to see the estimated usable capacity, overall storage efficiency, and how many drive failures the array can tolerate without data loss. This is a planning estimate; real-world usable space is slightly lower due to filesystem overhead and controller reserves, and RAID is not a substitute for backups.