Steam Server

If you need to create a new server and mount a storage volume with your games folder, just create a new directory and symlink the old one.

If you have already moved the folder adjust permissions:

sudo chmod a+rwx -R /foo/games

UFW Firewall

sudo ufw allow proto tcp from IP.ON.LAN to any port 27036,27037
sudo ufw allow proto udp from IP.ON.LAN to any port 27031,27036

Move Steam Data

Launch steam once to select the Download location because it needs to be an empty folder, exit steam and close it from background. Move all your Steam data to your bulk storage device.

Locate your Steam files cd / && sudo find -name steam. The /home/$USER/Steam folder is only for log files Downloaded data, client updates, etc.

mkdir /mnt/steam/SteamFiles
chown myuser:mygroup /mnt/steam/SteamFiles
cd ~
ln -s /mnt/steam/SteamFiles .steam