Cause and Effect – Warranties and Equipment Half-life.

Cause and effect is much discussed topic. People are always jumping to conclusions about causality, when all they know is that there is a correlation between two events.

XKCD even made a cute cartoon about this subject.

So this eternal question showed up for lunch today. We were discussing the recent epidemic of network equipment failures. Within a week we lost two switches and a router. Someone remarked that we probably purchased all this equipment at the same time, and the warranty on the equipment probably expired last week.

Everyone laughed. Because we all know that if you purchase something with 1 year warranty, the equipment is sure to fail after a year and a day.

But this started a chicken and egg discussion – do manufacturers build equipment that will last exactly a year and a day, or perhaps we they are setting the warranty time to be slightly lower than the mean time to failure of the equipment.

Both the senior DBA and I thought the answer was completely obvious. We just didn’t agree on which answer.

Senior DBA thought that manufacturing technology advanced to a point that it is very easy to build equipment that will last for very long times. However, since they only had incentive to offer warranties for around three years, they built the equipment so that it will fail shortly after the warranty expired.

I thought the opposite. Equipement durability is like SLAs – building something that will last 4 years is vastly more expensive than building something that will last 3 years. Also, I’m not sure that consumers take durability into account when deciding which brand to purchase. So, the manufacturers build something that can be profitable at a price the market will pay. Then they test or calculate how long it will continue operating on average, substract a month from that and call it their warranty.

We had a long and not very usefull discussion around that – each of us was so convinced that his point of view is completely obvious and could not understand how the other person (who is normally very smart) does not immediately see the obvious.

Any readers working in the manufacturing industry cares to shed some light on this mystery?

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2 Comments on “Cause and Effect – Warranties and Equipment Half-life.”

  1. joel garry says:

    Most companies track their returns, and have number crunchers calculate whether the cost of RMA’s is worthwhile.
    QA and financial people track the returns.

    Engineers designing systems try to use the cheapest parts they can, then do real world testing of samples. But it is difficult to properly simulate real real world conditions, and they don’t usually because there are too many possibilities. The variance in parts is less predictable than one would hope, especially with supply chains from, er, countries with different business cultures.

    However, when things get to your site, they are likely to be bought in batches, and then be subjected to similar environmental stresses. So you are both right.

    (I’ve worked at electronics, aircraft and pharmaceutical companies on their manufacturing software).

    I wish I could buy stuff that will last at home, especially routers and modems.

  2. prodlife says:

    Wow! Joel, thanks a bunch for the detailed information.

    Also, timely, as my home modem died last week 🙂


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