The mystery of Windows Experience Index fail to assess disk performance

I have posted this before on another blog space, but decide to repost it here as I intend to use this blog exclusively from now on.

So I bought a new Dell XPS laptop with core i7 running 64-bit Windows 7 almost a year ago.  After getting everything up and running, I couldn’t get Windows Experience Index (WEI) to compute the score and it kept failing at the very last step which was assessing the disk performance, saying something about data being invalid.  Granted this number doesn’t mean much, but still I felt as if something was missing.

To add to the confusion, the disk went bad within just a week (says a lot about the quality of XPS, which is supposed to be a high-end product line).  So at first, it seemed to make sense and I thought no wonder, because the disk was bad.  Then Dell sent out a technician and replaced the disk with a refurbished one (just like buying a new car, as soon as the machine left their warehouse, it started to lose its value and would only deserve refurbished replacement parts), but WEI still would not work.

Searching around a bit online and found a couple of other folks encountered the same problem, but there was no clear explanations nor solutions.  Finally I decided to bite the bullet and sent a help request to Microsoft’s customer support team.  The guy who got back to me immediately started to blame third-party software.  There are three words exactly describing how I felt when I saw his response: predictable, ignorant, and funny.  I guess it was their SOP to immediately pointing the finger at some unspecified “3rd party”, but what he didn’t know was that every time I get a new computer, I wipe out what came with it and do a clean installation using my own OS (a sincere thank to the deal between my university and Microsoft, we get Windows Ultimate edition at an extremely low price), so it was a clean installation of Windows 7 without any other software on it.  Even if it were true, that is, some 3rd party software indeed caused the problem, it didn’t make WEI look any better because it just show how vulnerable WEI can be.

As everything else seemed to be working fine, I decided to let it be since this WEI number really doesn’t mean anything.  Then just a few month ago, I saw another post complaining about this problem, but this time, the gentleman also found the cause.

Just like what I typically do, this gentleman re-installed his own Windows 7, but more importantly, he also moved all User directories to a different partition than C:\, and created symlinks on C:\ to point to the actual directories.  As it turns out, while the symlinks work fine for other applications, it does not work for WEI.  Instead, WEI relies on two environment variables TMP, and TEMP, to dump its I/O data, and by default, both TMP and TEMP point to the temporary directory within the AppData directory under each user.  Since the user directories are relocated to a different partition, and WEI doesn’t honor symlinks, it is unable to find the physical directory pointed to by the env vars and thus the error.  As soon as I reconfigured these two env vars to point to the physical temporary directories instead of through the symlink, WEI started to work.

So yes, keep blaming the 3rd party software.

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One comment on “The mystery of Windows Experience Index fail to assess disk performance

  1. Jon Turpin says:

    Excellent sleuthing sir. I had deduced the error was related to WEI’s inability to follow a symbolic link, but I hadn’t thought of the env vars.
    I just want to say thank you!
    -Jon T.

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