Interesting topic.
I keep all of my libraries on a dual-HDD NAS. Two 6GB Drives are in a RAID so they mirror each other for data protection.
I have dozens of CG Axis libraries, plus dozens of Evermotion. CG Axis is the best all-round, IMO, especially because they give you C4D + VRay along with MAX + VRay.
Anyway, I really only wanted to post about HOW I interact with these libraries. I recommend that you DO NOT UNZIP the whole model archive. It takes too much space to extract AND maintain all of the files. I do extract all of the textures to a folder in the same dir as the archive. This is for easy re-linking.
So, I keep the collection archives organized into appropriate named folders for clarity. I also put all of the PDF preview files into a separate directory, which is where I go to first look for a model visually.
When I pick a model from the PDF, I open the archive and extract only the file I need. Open it and re-link textures, then save it (outside of the archive) for future use. This method allows to keep the bulk of the collection in an archive, only grabbing then saving what I need after setting it up for my pipeline.
Ultimately, this saves space on the NAS, and has the added benefit of keeping the original in pure original form, while having an updated version for my needs.
While this helps me conserve space in the present, it doesn't really address keeping backups of such huge amount of data. My only hope is that both drives don't die at the same time!