I recently purchased a Roamio Pro with 3TB. Can I simply plug a eSATA drive into the back port to increase my drive capacity? If so, how does it work as far as space allocation? Some DVRs like the old Scientific Atlanta would use only the external drive while it was plugged in. When you unplugged it, it would revert back to the internal drive. How does the TiVo system work when adding an external drive? Can you choose which drive to record to? Is the external drive overflow from the internal? Can I use any external SATA drive. Any recommendations on a specific drive that is designed for this type of application? Thanks in advance.