RAID Calculator - Usable Capacity & Fault Tolerance for RAID 0, 1, 5, 6, 10
RAID Calculator
See how much space your array gives you and how many drives can fail
Eleven Layouts
RAID 0, 1, 5, 6, 10, 50 and 60, ZFS RAID-Z1 to Z3 and plain JBOD.
Fault Tolerance
See how many drives can fail: the number guaranteed, and the best case for nested arrays.
TB and TiB
Drive makers use decimal terabytes; your OS often shows binary tebibytes. Both are shown.
Full Privacy
Everything is calculated in your browser.
How RAID Capacity Works
Redundancy costs space. RAID 0 uses every drive but survives no failures; RAID 1 mirrors, so you keep one drive's worth however many you add; RAID 5 gives up one drive to parity and RAID 6 gives up two, so four 4 TB drives yield 12 TB in RAID 5 and 8 TB in RAID 6; RAID 10 mirrors pairs and stripes across them, keeping half. RAID 50 and 60 stripe across several RAID 5 or 6 groups, and ZFS RAID-Z1 to Z3 work like RAID 5 with one to three drives of parity.
RAID is not a backup: it protects against a drive failing, not against deletion, corruption or a fire. Large arrays also take a long time to rebuild, and a second failure during a rebuild can lose the array, which is why RAID 6 or RAID-Z2 is often preferred for big drives. Arrays use the smallest drive's size for every member, and file-system overhead reduces the usable space a little further.
Key Takeaways
- Hot spares: Spares are counted as raw space but not as capacity.
- Nested arrays: RAID 10, 50 and 60 show a guaranteed and a best-case failure count.
- Not a backup: Keep separate backups of anything important.