OT-ish - Long term storage solutions for Project folders

I was defragging my audio drive last night and noticed that it's getting a little crowded in there. Time to start archiving and removing my older projects that I'm no longer working on. At present, for my backup I have a USB harddrive that I just copy my Cakewalk audio projects folder onto - no compression, no backup software. This is a just a USB case and I can swap out the hard-drive if I want/need to, so in theory I could just get a new harddrive and store the present one as my archive.

What I'm wonder is, is this a viable and reliable solution for long-term archiving my project folders? I imagine some of these project folders are way to large to fit on a single CD, but would it be worth it to try to figure out a way to store them this way. CDs have failure factor that must be considered, right? Do hard-drives as well? Isn't there some issue with inactive harddrives freezing up?

Any thoughts are welcome.