Installing Kali with an additional HDD

I am installing kali and want to seek some clarification on some things-
I have 50GB unallocated in SSD and 50GB unallocated on HDD, I want to install my kali by merging these two drives.
If that is not possible then can I possibly install kali on 50GB SSD and add 50GB HHD to the logical partition. Merging should be such that I don't have to specify different areas for saving the files.

Kindly help me out with some resources or with some explanation regarding my query above.