Meet screen.
Connect through ssh, start screen. This open a virtual console emulator on top of the one provided by ssh. Start your server there.
Then press Ctrl-a, then d. This detach the screen session, keeping it running in the background.
To [R]e-attach to it, use screen -r.
If screen is not installed and you can’t install it, you can also start an application in the background by adding a & to the command, as you tried. But you should not close the terminal window then ; just disconnect, with the bash command exit, or Ctrl-d.
The advantage of screen is that you can still read the output from the server, in case there is an error or anything.
Screen is a really powerful tool, with many more commands. You can add a new virtual window with Ctrl-a, then c (for Create) ; switch through windows with Ctrl-a, then n (next) or p (previous), …
But you need it to be installed to use it. Since you seem to have root access, this shouldn’t be a problem.
EDIT: tmux is another great solution for the same use-case.