ServerBeat is a special protocol that will dynamically assign the specified IP between multiple CrushFTP servers. You specify an IP that is free for your Virtual IP. You then set any NAT port mapping or DNS records to point to that IP. The CrushFTP instances that are running configured for that virtual IP via ServerBeat will share the IP. Only one machine will have the IP at any time, and it will hold onto it unless its powered off. In that case, within just a few seconds, the other CrushFTP server will take over and start using the IP.

This is ideally suited for two machines in a failover scenario, but it could be used on 3 or 4 if you really wanted to. Still only one machine is active at any time. When Crush changes the IP, its changing it in the OS. Technically its assigning an IP alias for the machine.

On the General tab, the IP is the LAN IP of the current machine, and the port is a port number both machines will talk to each other on to decide who is master.
On the Advanced tab, the Virtual IP is the shared IP each machine will dynamically assign, and the second field is an ethernet index. Keep it as 1 unless your Linux/Solaris machine has a different index on it. eth0:2 for example.