I had an extra USB drive laying around and decided to back up all of the current isos on my mainly used drive to it, just as a good measure. I used WBFX Manager 3.0.1 and copied 49 images from one drive to the other, and initially everything appeared to be normal. Until I checked file sizes. The 49 images on my main drive equal to a little over 77GB. The 49 images copied to the backup drive is just a little over 75GB! I also noticed that each and every image copied to the backup drive is just slightly smaller than the image on the original source drive. For example, something like "Billy the Wizard" is reported on the source drive as 0.10GB, and on the destination backup drive as 0.09GB. So, I extracted the ISO drive the main drive of this particular game, removed it from the backup drive, and went to re-add it. Again, 0.09GB reported (even before adding). BUT, if I take the exact same iso extraction and apply it to add (I didn;t add it, just loaded it into the add queue), it reports as 0.10GB! For what it's worth, they both load off of both drives, so I guess that it is fine. But the real question is WHY the drastic change in file size between one drive and another? The main drive is a 500GB, and the backup drive is a 250GB. Could it be cluster size? I don't know for sure exactly HOW WBFS is managing the file system, so I am in the dark here. Just curious. If anybody knows, please fill me in!