If you add a second NetInstall server to a network, have your users reselect their NetBoot image in the Startup Disk preferences pane. This causes the NetInstall server load to be redistributed between the servers.
You can also force redistribution of the load by deleting the /var/db/bsdpd_clients file from the existing NetInstall server.
After deleting the bsdpd_clients file, the server doesn’t remember which clients selected which NetBoot or NetInstall volumes via Startup Disk. Unless the clients reselect their intended NetBoot or NetInstall volumes, the clients boot into the default image on the server.
Similarly, if you’re recovering from a server or infrastructure failure and your clients are starting up from a reduced number of NetInstall servers, delete the bsdpd_clients file from the running servers so clients can again start from among the entire set of servers.
The bsdpd_clients file holds the Ethernet MAC addresses of the computers that have selected the server as their NetInstall server.
As long as a client has an entry in an available server’s bsdpd_clients file, it always starts from that server. If that server becomes unavailable, the clients locate and associate themselves with an available server until you remove their entries (or the files) from their servers.
If a client is registered on more than one server because an unavailable server comes back on line, the client starts up from the server with the fewest number of clients that started from it.