Adding multiple external hard drives

Hi

I have a Dell XPS 8300 with 2 X 1TB internal hard drives operating Windows 7. Additionally, I have 2 X 2TB external hard drives connected to the main computer through 2 X eSATA ports (1 being part of the motherboard, the other via an additional internal card).

Both work perfectly independently, but not together. I can only access one drive at a time since they both use “Port 4”.

Is there any way I can see both drives at the same time to enable me to backup from one to the other? Or do I need to continually mount and unmount drives as I need them?

Thanks for any advice received

Roin