@
tanjamuse,
eschwartz - Sorry for the mislead
FreeFileSynch (FFS) is a good choice, the only things I would add are
It wont fix your current 'backup archive', so create a fresh mirror of your library. When you're happy with FFS then probably best to get rid of that 'backup archive'.
Make sure you know how to restore something from the FFS 'mirror'. Doing a backup is a means to an end, not an end in itself. The end is being able to do a restore when something goes wrong and you're anxious.
And why stop at your e-book library - are the other things you value backed up - photos, documents, emails, tax records etc.
BR