Anyone using time machine with a file vault encrypted MBA? i decided to go ahead and turn on file fault since if i did ever lose this laptop i would hate for someone to be able to get into it. just wondering how this affects backups on time machine. given the entire drive is encrypted how does the backup store data? does it incrementally store encrypted versions of the new stuff or does it have to do a complete rewrite of the entire drive every time? i have the 256gb drive mba11 so will i be ok getting a 500gb external drive to use for Timemachine?