Backup two internal drives onto one external drive
I have a desktop with an HDD I've used for several months. I want to add an SSD, clone the HDD (which is still mostly empty) onto it and make the SSD the boot drive. I've heard that I should backup the HDD before adding the SSD. After getting both internal drives working, I want to back up both of them regularly. Is it possible and practical to backup an internal SSD and HDD onto a single external HDD?