See
https://www.mobileread.com/forums/sho...d.php?t=238959
I think calibre may create some temporary folder/files within the library folder when books get moved & deleted - AFAIK you cant redirect where those folders and files are created. And IIRC the names of the folders and/or files are random strings 6 characters long that are generated as needed - eg hd5fny
The bottom line is that calibre as it stands today, is not designed to work on servers or network storage appliances.
BR