something like a large fan fiction library could be v hard to rebuild from scratch - so put an extra copy into cloud storage also, to be extra safe,
just pick one ( or more) of google drive, dropbox, one drive, amazon cloud drive... they all give you a few Gb for free.... and copy your entire calibre folder to there ( then don't forget the password!
then even if your entire PC goes up in flames, you still have that library !