the behavior is not different as if you would have your mydata.gz at the top of your drive because TC scans for a backup at each boot and load it automatically; what you can do, too, is to rename mydata.gz into mydata.tce, and place mydata.tce into another directory (not /tce); this way, you would then start without restoring your configuration at boot (f.ex. if you don't need your config. because you only want to perform some tasks in text mode as fetching data on remote servers or browse the net with a text browser, or listening to music with mplayer-nogui etc.), but you can restore it when you want/need it by mounting the mydata.tce as if it would be an extension among others (on the commande line: $ tce-load /your_directory/mydata.tce).