Would you use a portable hard drive such as a Seagate or Western Digital, 1TB or larger, as a secondary hard drive which would be left plugged in on a 24/7 basis? USB, of course.
My prior desktop, which is a two-hard-drive tower and I could have up and running in minutes, was used as installing programs-only on C:\ and documents/downloads created on D:\. It was easy to backup the C: drive in case of disaster, i.e., hard drive failure, and backing up the D: drive was much easier also in case of disaster.
It's not that I don't back up the two folders I use all the time religiously (D