Jellyfin: The Free Software Media System

Don't do it. I did it for a while it's very slow and hard on the weak little CPU in the router. Eventually the USB port burned out entirely.

I don't use that kind of setup but in general it depends on several factors.

Is your server with Jellyfin on connected to this via wifi or ethernet. If wifi then the connnection quality and speed may matter, if your client needs to have Jellyfin do the trandcoding this might be an issue if its a bad wifi connection. Also if you have high quality content, like 4k resolution, that gets streamed directly this might also be a bottleneck if it goes via wifi.

Also depends how many simultaneous users you will have, for one user this might all be good, but once two or three share the connection it might create issues.

I run my Jellyfin server with 2 network hard drives. It's a perfectly fine way to do it.

Do note however that you'll need a third device to actually run the Jellyfin server. Jellyfin for Android is a client app. The Jellyfin server can be run on ARM devices if they are running Linux, but not on Android.

One question: Is there any specific reason for not plugging that hard disk in the same server that is hosting Jellyfin?