Jellyfin performance on Synology

[TheDreadPirate]

If it was busy generating trick plays or chapter image extraction, those usually may appear in the dashboard as an active job. But your log would show what activity is going on. Regardless, the disk IO for a database easily saturates a HDD.

What you can do in the meantime is to limit the number of library scan threads.

Dashboard > General. Set both "Parallel library scan tasks limit" and "Parallel image encoding limit" to 1.

If you intend to keep the NAS, I'd choose a mini PC with an N100 over a 5700U. The media engine in the N100 is MUCH better than the 5700U.

If you intend to build a proper server, including having storage be locally attached, we'd need a budget and intended usage to give more specific recommendations.