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How Is MTBF for the Network Time Servers Calculated?
A simple definition of Mean Time Between Failure (MTBF) is:
Total hours of operation of the product ÷ Number of product failures
EndRun Technologies has been shipping rackmount time servers since early 2001. If we assume that most
of the units shipped have been operating most of the time that equals the total hours of operation. Divide
that by the number of failures that have occurred over the years and it yields a number greater than
2,000,000 hours (228 years).
The reason we don't claim an MTBF of 2,000,000 hours is because it is better to take into account the
measurement time period in order to increase confidence in the claim. In our case the measurement period
has been about 5 years (since early 2001). If we lower our number from 2,000,000 hours to 225,000 hours
(25 years) then our actual measurement period (5 years) is 20% of that. This is conservative enough to
guarantee that the reliability of the product will continue to exceed the MTBF claim.
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