Currently I keep my time machine backup on an external usb hard drive which is a seagate hd in an enclosure I bought a while ago. I want to maintain a second copy of the time machine back up. Is it better to buy an external RAID enclosure, put the current drive in there, get another drive, and then just have time machine backup to that drive? Or should I just get another enclosure and another drive? If I do it this way, can I automate the time machine backups across two drives in any way, or I have to manually run it twice?