RAID Calculator
Find the usable capacity, fault tolerance and speed of a RAID array from its level, drives and drive size.
Drives and RAID level
Count only the drives that hold data or parity. Hot spares sit idle until a drive fails, so they are not part of the capacity. RAID 50 and 60 split the drives into equal groups, and each group is its own RAID 5 or RAID 6. RAID protects against drive failure, not against deleted files, ransomware or fire, so it does not replace a backup.
Drive speed
These are typical figures for each drive type. For a firm number, use the sequential speed and random IOPS from the drive's spec sheet. Editing either number switches the drive type to Custom.
Result
| Array | Value |
|---|
| Measure | Value |
|---|
| Level | Usable | Efficiency | Failures survived |
|---|
Speeds are best-case rules of thumb: sequential speed scales with the drives that carry data, and each write to a parity array costs extra reads and writes (a penalty of 2 for RAID 1 and 10, 4 for RAID 5 and 50, and 6 for RAID 6 and 60). Real arrays are slower because of controller limits, caching, rebuilds and workload mix. Failures survived shows the number the array is guaranteed to survive, and the most it could survive if the failures land in different mirrors or groups. TB means 1,000 GB and TiB means 1,024 GiB, which is how operating systems report size.