proxmox+jellfin+WD

[Tim]

What @TheDreadPirate meant is that you can add the path to the content on the new drive to an already existing library within Jellyfin. Select the manage library option when clicking on the 3 dots on the Libraries dashboard page, a modal with settings of the library shows up and click on the "+" button next to "Folders".

I am not familiar with proxmox containers, but if it works like Docker, then you need to configure a mount to the new data directory on your 4TB WD MyCloud EX2 Ultra as well. This way you allow the container to use the data inside your mounted path that is outside your container.