Friday, May 6, 2011

Obviously Wrong

I got an email from a vendor today, saying, "This performance test is taking far longer than it normally does. Here's a screenshot. What should we do?" In the screenshot, it showed the following speed and completion percentage for a linear write on a standard hard drive:

linear write 27.89% 1.8 MBps

No, that is not a typo.

Now here's a case where something is obviously wrong. There's no way a modern hard drive should be seeing write rates anywhere near that slow. I don't know what's wrong. Perhaps there's a bad part in there (backplane? motherboard? cpu?). Perhaps the box was built incorrectly and some cable isn't plugged in properly somewhere, or the CPU isn't seated correctly.

The point is that it doesn't matter. When something is obviously wrong, there's no need to continue to follow your plan. You can skip ahead to the "it's broken, now what" part. That holds true for tests like this one, for prototypes, or whatever you're doing. If it's meant to show a result, you can stop as soon as you see a result, even if you thought you'd have to get a little farther down the path before an answer presented itself.

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