RAID capacity calculator
Every RAID level trades capacity for redundancy or speed. The arithmetic is simple; the consequences are not.
Usable capacity
20.000TB
- Raw capacity
- 24.000
- Capacity given to redundancy
- 4.000
- Storage efficiency
- 83.33 %
- Drives that can fail For RAID 10 this is the best case; two failures in the same mirror still lose the array.
- 1
- Rough read-speed multiplier
- 5.0
- Minimum drives for this level
- 3
Show the working
- Number of drives = 6
- Size of each drive = 4
- RAID level = 5
- usable_drives = 5 == 0 ? 6 : 5 == 1 ? 1 : 5 == 5 ? 6 - 1 : 5 == 6 ? 6 - 2 : floor(6/2) = 5
- Usable capacity = max(5, 0) * 4 = 20
- Raw capacity = 6 * 4 = 24
- Storage efficiency = 24 > 0 ? 20 / 24 * 100 : 0 = 83.3333
- Drives that can fail = 5 == 0 ? 0 : 5 == 1 ? 6 - 1 : 5 == 5 ? 1 : 5 == 6 ? 2 : floor(6/2) = 1
- Rough read-speed multiplier = 5 == 1 ? 6 : 5 == 10 ? 6 : max(5, 1) = 5
- Capacity given to redundancy = 24 - 20 = 4
- Minimum drives for this level = 5 == 0 ? 2 : 5 == 1 ? 2 : 5 == 5 ? 3 : 5 == 6 ? 4 : 4 = 3
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- RAID 0: usable = n x size
- RAID 1: usable = size
- RAID 5: usable = (n - 1) x size
- RAID 6: usable = (n - 2) x size
- RAID 10: usable = floor(n/2) x size
RAID is not a backup. It protects against drive failure, not against deletion, corruption, ransomware or fire.
Rebuilding a large RAID 5 array stresses every remaining drive for hours, which is why RAID 6 is preferred above about 6 TB per drive.