Originally Posted by dcarlozzi
Thank you for the reply. So, let's say, if I add one new book to my library on my desktop, I go into the desktop Calibre folder and copy the new book folder and the metadata file (icon) and just past them into the Calibre backup folder on the USB drive and that will do it?
In theory, yes. That said, there is a lot of room for error. For example, your method will not deal with deleted books, converted books, or books with changed authors or titles.
You would be much better off using a replicator to copy the calibre folder structure. These programs will look for changes and copy only the files that need to be copied. Most of them can (optionally) delete files that have been removed from the source. If you are using Windows, then free ones I have used are xcopy, Microsoft synctoy, and Karen's Replicator (which I prefer because of its good logging), but there are many more. Some replicators support scheduling, if that is of interest.
First set up the source and target folders in the replicator. Then to make a copy, stop calibre, then run the replicator. Your USB storage will then have an accurate copy.