RAID Storage Calculator
Choose a drive count, capacity, and RAID level to see exactly how much usable space you get, how many drives can fail safely, and how long a rebuild takes. Compare all levels side by side before you buy. Nothing uploaded.
Drive configuration
Results
All RAID levels compared - same drives
| Level | Usable | Efficiency | Drive failures tolerated | Rebuild time |
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Learn more: RAID storage design and planning
Why storage efficiency varies so much between RAID levels
RAID 0 gives you 100% efficiency with zero fault tolerance. RAID 1 mirrors every byte so you only use 50% of your raw storage. RAID 5 strikes a balance: for 4 drives you get 75% efficiency and can lose one drive. RAID 6 uses two parity drives - with 6 drives you get 67% efficiency but survive two simultaneous failures.
How to use the RAID calculator
Set drive count and capacity using the dropdown and +/- buttons. Choose a RAID level and see usable space, efficiency, fault tolerance, and estimated rebuild time at 200 MB/s. Compare all valid RAID configurations for your drive count side by side in the comparison table.
FAQ
How much usable space does RAID 5 give me?
RAID 5 gives you (n-1) x drive size usable space, where n is the number of drives. For 4 drives of 4 TB each, you get 3 x 4 = 12 TB usable from 16 TB raw, an efficiency of 75%. One drive can fail without data loss.
What is the difference between RAID 5 and RAID 6?
RAID 5 uses one parity drive and can survive one drive failure. RAID 6 uses two parity drives and can survive two simultaneous drive failures. RAID 6 requires a minimum of 4 drives versus 3 for RAID 5, and storage efficiency is lower since two drives are used for parity.
How long does a RAID 5 rebuild take?
Rebuild time depends on drive capacity and rebuild speed. A 4 TB drive rebuilding at a typical 200 MB/s takes about 5.6 hours. Larger drives take proportionally longer. During the rebuild window the array is vulnerable to a second drive failure, which is why RAID 6 is preferred for large drives.