Can I add an eSATA drive if I previously upgraded the hard drive in my TiVo?
The new “plug and play” eSATA expansion support does not work if you upgrade the built-in drive on the TiVoHD and Series3. You can still add an eSATA drive to an upgraded TiVo, but doing so requires you to open the box and void the warranty. Instructions to do that can be found in Section IV, #10 of this FAQ.