RAID Fault Tolerance Calculator
Compares how well RAID levels cope with failed disks.
Failures always survived
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Chance of surviving those failures — %
All levels with this many disks
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The formula
RAID 5 survives 1, RAID 6 survives 2 RAID 10 chance = Π (n − 2i) ÷ (n − i), for i from 0 to k − 1
RAID 10 can lose several disks as long as no mirror pair loses both, so it has a chance rather than a fixed limit above one failure.
What to watch out for
The table covers simple RAID 10 built from two-way mirrors.
Frequently Asked Questions
Can RAID 10 survive two failed disks?
Sometimes. With 6 disks the chance is 80%, because the second failure must miss the first disk’s mirror.
Is RAID 6 safer than RAID 10?
For two failures, yes: RAID 6 always survives them. RAID 10 usually rebuilds faster, because it copies from one mirror.