I have a 3TB My Book live that I've been playing with. I can get the Gentoo system to compile correctly (modified the partition layout a little and increased the swap size).
Unfortunately, I can not get it to find the SATA controller. I was wondering if I'm even using the correct controller to begin with. I am using Kernel 3.10.10.
BTW: I have a 32MB /boot (sda1), a 1GB swap (sda2), a 8GB / (sda3), and the rest for /mnt/data (sda4). I did leave a ~512MB chunk for a rescue area (sda5) at the end if needed.