[Adoby]

You can use a sync utility. I use rsync in Linux for similar purposes.

That way only changes have to be copied. Make sure Calibre is not running while the sync is being done.

I use rsync to update a backup copy of the Calibre library every time I reboot. Also I use this backup copy to update the library for a virtual instance of the Calibre server. Every time I start the virtual machine, with the Calibre server, the library is updated from the backup copy, also using rsync. So I have three copies of the Calibre library. One copy I update, one backup and one copy of the backup that is used by the Calibre server. In this way each sync can be done independently and automatically, without having to manually shut down Calibre on the other machine.

Note that my setup only copies changes in one direction. It cannot sync changes that happens at both machines. If anything is changed on the virtual machine, those changes are overwritten the next sync.

Google "sync utility windows" for ideas about suitable programs.