I just had a similar problem, nearly filled the hub with my media I spent a few months ripping, so I bought a cheap 2 TB external WD elements drive to add more space and back up the HUB drive, as I didn’t want to go through the ripping again to rebuild it if I lost the drive.
I kept my movies directory (about 650GB) on the WD live hub 1 TB internal drive, I’ve moved my TV Series,music & pictures (about 350GB worth) to the external USB drive plugged into the hub.
I created a directory on the external USB drive called .backup, the WD ignores this directory for the media library as it is a hidden directory starting with fullstop (had to use DOS command MKDIR for this as explorer doesn’t like creating files starting . I made a copy of the movies directory from the hub to the external USB drive .backup directory (did this on the hub copy directory option which is much faster than using via network PC).
I made a copy of the TV Series/music/picture directories onto my PC.
I now use a PC package called Puresync, which is freeware for personal usage, to synchronise the directories between the HUB/USB/PC, you can set it up on lots of events or time, I just do it manually, as I’m not adding that much media now its setup, the occassional movie, picture or CD. If the drive crashes on the hub, or media is deleted by mistake, I have copies on the external USB or PC, if I lose the drive on the external USB or PC, I have copies on the other drives.
I had abit of media compiling as I moved files around, the only other problem I found was that the sort by folder option does not show all the media on the hub, I have to go into the Hub drive or the USB external drive, If i remove the folder filter, it shows all the media on both drives, but removes the folder structure, so its really messy and takes allot longer browsing media, so the way I have it set is filter by folder, choose Hub for Movies, external drive for TV Series, Music & Pictures.