Apple Mac OS X Server (version 10.2.3 or later) - Manual (Page 537)

NetBoot 537
Load Balancing
NetBoot provides a significant benefit to those system administrators tasked with
maintaining a large number of Macintosh computers by having all of those computers boot
from the same system software image. This feature, however, makes it critical that the
NetBoot server remain available to the client computer relying upon it. To provide
responsive and reliable NetBoot service, you should set up redundant NetBoot servers in
your network infrastructure.
Most sites using NetBoot achieve acceptable responsiveness by staggering the boot times of
client computers in order to reduce network load. Generally, there isn’t a need to boot all
client computers at exactly the same time; rather, client computers are booted early in the
morning and just remain booted throughout the work day. For clients computers running
Mac OS 9, you can program staggered startup times using the Energy Saver control panel.
(There is no equivalent feature in Mac OS X, however.)
If heavy usage and simultaneous client startups are overloading the NetBoot server and
causing delays, consider adding additional NetBoot servers to distribute the demands of the
client computers across multiple servers (load balancing). When incorporating multiple
NetBoot servers, it is important to use switches, as the shared nature of hubs creates a single
shared network on which additional servers would have to vie for time.
Enabling Server Selection
If you add a second NetBoot server to a network that has a single server already in use, have
your clients reselect their boot image in the Startup Disk control panel or preferences pane.
This causes the NetBoot load to be redistributed among the servers. You can also force
redistribution of the load by deleting the file /var/db/bsdpd_clients from the existing
NetBoot server. This enables clients to select which server they will use as their NetBoot
server. Similarly, if you are recovering from a server or infrastructure failure, and your clients
have been booting from a reduced number of NetBoot servers, you will need to delete the
bsdpd_clients file from the running servers so that clients can once again spread out across
the entire set of servers.
The bsdpd_clients file on any given server holds the Ethernet Media Access Control (MAC)
addresses of the machines that have selected this server as their NetBoot server. As long as a
client has an entry in an available server bsdpd_clients file, it will always boot from that
server. If that server should become unavailable to those clients, they will locate and
associate themselves with an available server until such time as you remove their entries (or
the entire files) from their servers. (If a client ends up being registered on more than one
server because an unavailable server comes back on line, the client boots from the server
with the fewest number of clients booted off of it.)
LL0395.Book Page 537 Wednesday, November 20, 2002 11:44 AM