so I had an external 500GB Western Digital MyBook and it is full. So I bought a 1TB Western Digital MyBook. The 500GB was in a case with esata, USB and FW800 and the new 1TB had only USB. So I swapped the 500GB and the 1TB so that my 1TB disk can use the FW800 interface. However the disks are not recognized as formatted disks with data on them. I have to initialize both of them although both are sata disks and work in their original case just fine. Only when I swap them out I have to format them. I did this for the new 1TB disk in the esata/FW800 case because it was new and empty and it works just fine now. But the old 500GB HD is full of data and I don't want to format it. How can I tell my mac that this disk is already formatted? Why can't I just swap SATA disks between SATA cases? Thanks for any help.