Steve Gibson from Gibson Research Corporation ran several benchmark tests against TrueCrypt 5 and has a theory that Windows might actually run faster with whole disk encryption than without. Recently on Security Now episode #133 Steve explains to Leo Laporte what he did, here is an excerpt from the podcast:

Steve: I don’t know. It’s like, okay. So I wrote a little batch file using that EndTimer tool and the Windows defrag and Vopt and Windows defrag. I ran those three in sequence. With no encryption, Windows defrag took 8 minutes and 35.765 seconds. Vopt took 4 minutes and 31.046 seconds. And then a final Windows defrag took 1 minute, 54.765 seconds. Okay, so just look at the first number, 8 minutes and 35 seconds. I did it; I did it again. That is, I restored the image, ran the script again, and it was 9 minutes and 1 second. So, you know, about 8 minutes and 45 seconds on average. And the difference are just we’re doing a lot of head-seeking. And so where the disk’s rotation happens to be is going to affect timing a little bit.

Steve: Okay. So it’s like, okay. So I’m seeing, like, 8.5 to 9 minutes to do the first defrag of a very well-fragged image. And this is the image where I went from Service Pack 2 and applied those 95 patches and rebooted a whole bunch of times. So, I mean, it mangled up the drive, so it was nicely fragged. Okay, then I restored that image, the superfragged image. And I encrypted it. Then I ran the defragger in the encrypted system. The first time it took 6 minutes and 13.531 seconds, down from 8.5 or 9.

Leo questions how this could be true… Steve offers up his explanation:

Leo: So do you have a theory for why this is doing that?

Leo: That’s just amazing. And great. I love it.