RAID Capacity Calculator
Enter how many disks you have and their size to compare usable capacity and failure tolerance across RAID levels.
How it works
RAID 0 stripes data for speed with no redundancy. RAID 1 mirrors disks. RAID 5 stripes with one disk of parity and survives one failure. RAID 6 uses two parity disks and survives two failures. RAID 10 stripes across mirrored pairs and survives at least one failure (more if they are in different pairs).
Capacity figures assume equal-sized disks and ignore filesystem overhead. RAID is not a backup: it protects against disk failure, not deletion, corruption or ransomware.
Frequently asked questions
Is RAID a backup?
No. It keeps a system running through disk failures, but accidental deletion and ransomware affect every disk. Keep separate backups.
Which RAID level is best?
RAID 6 or RAID 10 for most servers with important data; RAID 5 is risky with very large disks because rebuilds take long.
Can I mix disk sizes?
Most RAID setups use the smallest disk's size for every member, wasting the extra space.