RAID Calculator
Calculate usable capacity, the number of disk failures survived and relative read and write speed for RAID 0, 1, 5, 6 and 10.
Free · No sign-up · Your inputs stay in your browser
Input
Calculate RAID capacity and fault tolerance
Output
32 TB usable
Raw capacity
48 TB
67% efficiency
Disk failures survived
2
Relative read / write
4.0× / 1.0×
Throughput versus one disk for large sequential I/O; small random writes on parity RAID are slower still.
Two disks' worth of parity: survives a second failure during a rebuild. The sensible parity level for large drives. Sizes are as drives are sold (decimal); the operating system will report about 9% less in TiB. RAID is not a backup: deletion, ransomware and a bad controller are copied to every disk.
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About this tool
Method, assumptions, practical next steps, and limits.
Choosing a level
RAID 1 and 10 mirror, so they lose half the capacity but rebuild quickly and write fast; databases usually use RAID 10. RAID 5 and 6 store parity, which is space-efficient but slow for small random writes. With today's large disks, a RAID 5 rebuild reads every other disk in full and one more failure or unreadable sector during that time loses the array, which is why RAID 6 is preferred. Linux software RAID is managed with mdadm.
RAID is not a backup
Every disk in an array receives the same writes, so a deleted table, ransomware or a filesystem bug is copied instantly to all of them. Keep separate, versioned backups.