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I've been looking into purchasing some switches for a new office fitout, and I notice that Netgear give their MTBF as 45 years (!).

How do they figure this out? Is this number meaningless? I assume they didn't get 1000 switches and run them for 45 years to see how many fail.

Given that an MTBF of 45 years is incomprehenable for this kind of device, is this number even worth paying attention to?

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Calvin's dad explains: i.imgur.com/0EYY5.gif –  MattB Mar 2 '10 at 21:28
    
That's probably the most accurate explanation (at least for IT equipment MTBF). That plus "really if it lasts 10 years they're gonna be replacing it anyway, it's IT gear!" –  voretaq7 Mar 2 '10 at 21:40
    
Haha, I'll have to bookmark that comic –  Mark Henderson Mar 2 '10 at 21:48

3 Answers 3

up vote 3 down vote accepted

I believe they base this figure on the MTBF for the components that they used to make the product.

Manufactures do not do this but if you look at how you actually calculate the reliability of a system you'll see that the MTBF of a system is not just the average or the lowest rated MTBF of the components that make up the system. To make anything with more than one part that will continue to function for 45 years is pretty much impossible.

So yeah I would take the manufactures number with a huge grain of salt.

Edit: I edited my answer so hopefully it's clearer on what manufactures of equipment do and how you actually calculate the reliability of a system. Which is something that manufactures do not do.

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"anything with more than one part that will continue to function for 45 years" - seems like that;s only true in the electronics world :\ –  warren May 1 '11 at 3:58

Google is your friend, here's a good article (the cached version, the site doesn't seem to carry the article any more):

http://74.125.155.132/search?q=cache:http://www.evaluationengineering.com/archive/articles/0500analyz.htm

Actually, here's a better article, from an old comp.arch.storage FAQ:

http://www.faqs.org/faqs/arch-storage/part2/section-151.html#ixzz0h3fetZJv

Here's the critical point:

MTBF is, therefore an excellent characteristic for determining how many spare hard drives are needed to support 1000 PC's, but a poor characteristic for guiding you on when you should change your hard drive to avoid a crash.

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Thanks. My google-fu has been weak lately... –  Mark Henderson Mar 2 '10 at 21:53
    
Wikipedia's article about MTBF is lousy, but it did have the link to the comp.arch.storage FAQ. –  Ward Mar 2 '10 at 21:58

An electronically-inclined friend once told me that they calculate the MTBF for individual components by testing them at high temperature, starting at a temperature so high that it fails after a few minutes and then reducing the heat and extending the graph down to room temperature. I have no idea how this leads to the MTBF for the whole router/hard drive/whatever, though; perhaps something like 3dinfluence suggests.

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No I agree with what you said. I probably should have said this in my answer. But I work for an electrical engineering company and we've designed equipment for EqualLogic, Juniper, and Nortel. Part of the specifications when building something is MTBF. And the way you make something with a MTBF of 5 years is to use resistors, etc that have a MTBF of 5 years. But like I said in my answer it's not a good measurement of the actual reliability of a device as a whole. –  3dinfluence Mar 2 '10 at 21:53

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