[Adoby]

One way to handle the use case in the first post, server on one computer, update on another, is to simply copy the calibre library. After editing/adding books on the fast computer, copy the whole library over to the server, replacing the old library. Possibly using a sync app to make it faster.

That way you can access the calibre library from both computers and have a backup as well.

Treat the backup on the server as a read-only copy.

You could have two copies on the server to avoid writing to the calibre library when the server is running. One copy that the server is using. One copy that is updated from the fast computer. And update th copy the server is using when the server is (re-)started. Perhaps using some scheduler? Or a "trigger file" added when the backup is updated.