I have 1 TM backup for my rMBP that will no longer backup. I still have access to the data and can TM back, but I get error messages when it attempts a backup and then the drive becomes unrecognizable. Power down drive, plug it back in, run disk utility and it's fine. Try a TM backup, same error. I've tried trashing the TM pref file but still nothing. I'll take any thoughts on the matter, but that's not what I'm asking about. I have another TM backup for my iMac that is full. Ideally, I'd like to have a 3TB drive, partitioned in 2. Copy existing TM backups, and have drive either hardwired (USB 2) to always on iMac and shared partition to rMBP, or shared via USB 3 on my router. I do also have cloned drives, and use crashplan.