hi i have an imac 27 with standard 1tb hdd. i use an external thunderbolt ssd with osx on it and the 1tb hdd as additional space. today i got the new 27 retina with 2tb fusion drive in it. ill still use the thunderbolt ssd as primary drive as i often switch it to macbook air. what will happen if i format the fusion drive?? it will still be seen by os as an 2tb drive or ill have twho separate drives (ssd+hd)???