You have to enlighten me how it could be a different physical server and yet be the same hard drive ?

Unless you are suggesting they use ATA-over-ethernet or something like that to share the same drive.

Or maybe you meant to be worried that they might use virtual machines where one is running the .gov site and the other would be mail server or something like that ?

At the volumes of web traffic they receive there it would surprise me if they only had one server to do just whitehouse.gov, especially if they're using drupal.