I have managed to copy with rsync and getting 180 MB/s. I guess my initial assumption was wrong, HDD is obviously not bottleneck here, it can get close to ISP speed. Thank you for pointing this out, Ill do more testing these days. Im kinda shocked because I never knew HDD can be that fast. Gonna reread all the comments as well

Yeah, but need to figure out how to see transfer speed using ssh. Sorry noob here :)

Its the cheapest drive I could find (refurbished seagate from amazon), I thought thats the reason for being slow, but wasnt aware its that low. Im also getting 25-40 MB/s (200-320 Mbps) when copying files from this drive over network. Streaming works great so its not too slow at all. Is there better way of debugging this? What speeds can I expect from good drive or best drive?

Ill research more about BTRFS and ZFS, thx

But that would first download to SSD, then move to HDD and then become available (arr import) on jellyfin server, making it slower than not using SSD. Am I missing something?

Its that simple to use different IPs just with DNS server:

DNS server

192.xxx.x.47 -> plex.yourdomain.xyz
192.xxx.x.53 -> snapdrop.yourdomain.xyz

But dont you have your services on the same IP and different ports? If thats the case you will also need reverse proxy like nginx. So DNS server will point your domain name (you can just make a name for local use) to your server IP. Then reverse proxy can point each name to a specific IP and port.

Reverse proxy

192.xxx.x.47:32400 -> plex.yourdomain.xyz
192.xxx.x.47:8080 -> snapdrop.yourdomain.xyz