Use MFSTools 3.2 to copy both drives to a new single larger internal drive.
MFS Tools 3.2
Thank you. I didn't realize it was possible to copy the recordings that are stripped across my internal and external drives onto a new bigger single drive. As I mentioned before, Weaknees told me this wasn't possible. Not sure why, I don't doubt their technical expertise.
So the procedure is:
1) create MSFTools boot CD or USB drive;
2) power off Tivo, disconnect DVR Expander and remove internal hard drive and connect them to PC with the new target drive. The Tivo internal drive and new target drive should be connected to the PC via SATA while the DVR Expander can be connected to the PC using its USB port (ESATA port on PC is not required);
3) Boot to MSFTools, login as root, password is tivo;
4) Enter command mfscopy -a /dev/sdX:/dev/sdY /dev/sdZ where sdX is the original internal drive, sdY is the original external drive and sdZ is the target 2TB drive;
5) Copying finishes several hours later, reinstall the target hard drive in the Tivo HD and restart. If everything worked, the Tivo should start with all the recordings preserved and the bigger capacity.
If something doesn't work, can I reinstall the old Tivo internal drive and DVR Expander and get that working again? Or does uninstalling and separating them break the link between them and erase everything on them if I reinstalled them back into the Tivo?
And would copying and replacing the old drives with the new one be treated as a service activation? My Tivo HD does not have lifetime service plan so I'm not sure if installing the new drive would be a service activation for Tivo and not allowed, in which case, this pathway isn't available to me.