Syncthing is probably a good choice

If you want the instances to sync, you just need to sync the directory. (I currently use nextcloud sync for this, but in the past I used synching and before that btsync)

If they dont try to modify the files at the same time (with sync delay) there won't be any issues. If they do grow out of sync, you can fix pretty easily with db repair.

I have my books on a remote share managed with a local calibre install on my desktop for easy transfer

Pretty sure you can just manage a remote library from the app, you just gotta point it at your library folder iirc. Also just found COPS, which I've never heard of but now I want lol.

I guess I never thought of this sort of option. I run Calibre in a docker container on my unraid server. Any books I add are sent over via FTP from whatever device I'm on at the time. I do still have to go into the Calibre instance and add the book. I believe there's a way to have it watch a folder for new items but not sure.

New Lemmy Post: How to sync local and remote calibre servers (https://lemmy.world/post/12977980)
Tagging: #SelfHosted

(Replying in the OP of this thread (NOT THIS BOT!) will appear as a comment in the lemmy discussion.)

I am a FOSS bot. Check my README: https://github.com/db0/lemmy-tagginator/blob/main/README.md