Hey there, @Bruce_22!
This is not an efficient way to use this HDD. I'd suggest you consider putting it in an external enclosure if you plan to use it as a backup/image drive. Remember that "backup" means that you have your data stored in at least two (2) locations. Moving data from your system drive to another internal HDD or an external hard drive is not a backup, unless there is already a duplicate of the file on a different drive. Meaning that keep you files on your system and copy them somewhere off-site as well to prevent potential data loss.
It's not a common practice to keep backups on a different HDD inside your computer because it's not efficient. For example, in an unfortunate situation where your whole system fails or gets fried, you will lose the data from both drives anyway.
If you don't have enough space on your system drive, I'd simply use the secondary one as a massive storage drive for big media files or other less demanding software tools (in case your primary drive is an SSD).
Let me know if you have more questions. I hope this helps you, though.

SuperSoph_WD