Making Sense of Reliability Specifications
“The drive maker is claiming 1,000,000 hours MTBF. That’s 114 years! Do they really think that’s a legitimate specification?” Yes! It is. We have heard this concern and comments like it many, many times over the years, and have seen it appear on tech industry forums and on Wikipedia.
Legitimacy of Specifications
We can explain why this spec is legitimate. The truth is, hard drives exceed their MTBF specs in many cases. We encourage you to download and read our 23-slide presentation on hard drive reliability specifications, to better understand this confusing subject.
Key Metrics Explained
We’ll explain why “Mean Time Between Failures” and “Useful Design Life” are not at all the same thing, in fact, they are totally unrelated. We’ll also take a look at reliability test setup and execution, and the basic methods for calculating the key reliability metrics. Then, we’ll discuss these key metrics and provide a practical definition, so you can better comprehend what the drive makers have done, and why.
Comparing Reliability
Another way to look at drive reliability specifications is to simply compare them. This way, at least you will know the relative reliability advantage or disadvantage each drive presents. An example: the difference in reliability of a high capacity, mainstream enterprise-class hard drive (1.2M hours MTBF) and that of an AV/Surveillance-class drive (1.0M hours MTBF) is 18%*. The same can be done with the related specification, Annual Failure Rate, of course.