I have and use Calibre, both on Windows 7 as well as Mac OS X (Mavericks). Unfortunately, both of these platforms contain distinctly different content including many DRM-free I've downloaded. Admittedly there is much about Kovid's excellent program I am still unfamiliar with, like backing up, which is why I'm asking.
Maybe it's me (using incorrect search syntax) but I was unable to find out how to back up using the
https://calibre-ebook.com link you provided. Come to think of it, I'm sure I've tried in the past but gave up after repeated attempts proved unsuccessful.