@
pghaworth - you might want to consider backing up your preferences, plugin settings etc, see
How do I backup calibre?
Because the library export feature includes the configuration folder some people prefer to use that for backup.
My daily backup job includes my calibre libraries and configuration folder along with all my other data - like tax receipts, photos, image editor settings etc. I use an incremental backup process: so, a) it's quick, and b) it means I can restore individual files, such as a specific plugin's configuration settings or a individual format file.
BR