I am setting up Ubuntu and just got to the option about using LVM to partition the hard drives. My understanding is that if I do this Ubuntu will be able to treat the two drives as one. That's great, but I also want to able to distinguish between the two drives because one is a solid state and one is not. Will I still be able to have a C and D drive with LVM, i.e. can I intentionally save a file to one verses the other?
You will indeed be able to choose where the logical volumes take their physical extents from. For illustration (taken from shell history):
sudo lvcreate VG -n LogicalName --alloc cling -L 500M /dev/dev0
The above flags can also be passed to lvchange when the volume already exists. This will move data from one disk to another:
sudo pvmove -n LogicalName /dev/dev0 /dev/dev1
Also, to avoid micromanagement of which file goes on which drive, I recommend running bcache on top of LVM.