Sun Microsystems SunLink SNA 9.1 PU2.1, Configuration Manual

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1-20 SunLink SNA 9.1 PU2.1 Server Configuration Guide—August 1997
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Each manager system automatically sets up a connection to each of the other
manager systems. When more than 50% of the manager systems are in contact
with each other, a quorum is established and the software automatically selects
one of the manager systems to be the primary manager system. The other
manager systems are secondary manager systems. When you connect to the
Sun PU2.1 SNA Server from the SunGMI, the Sun Name Server routes your
connection to the primary manager.
Only the primary manager system can make changes to configurations. When
you make a configuration change and save it, the primary manager system
updates the configuration database and distributes the updated configuration
to all the other manager systems in the network using a 2-phase commit
protocol. Since the complete configuration is replicated on each manager
system, data is not lost if a manager system fails, and service is not interrupted
while a backup is restored.
Both the primary manager system and the secondary manager systems can
update the status of resources, distribute event information, handle DNS
requests and return the IP addresses of the system where the specified
resource can be found, and perform load balancing. If a manager system is
located in each physical site, requests for resource location and load balancing
can be handled by the local manager system, reducing the time delay for client
requests.
If a manager system loses contact with the others, the manager network
continues to operate provided that a quorum is maintained among the
remaining manager systems. This prevents two (or more) disconnected
fragments of the manager network from attempting to manage the Sun PU2.1
SNA Server at the same time. If a quorum cannot be established, configuration
capability is disabled and only DNS requests can be performed. This
guarantees that the distributed database is correct at all times.
If the primary manager system fails and the remaining manager systems can
establish a quorum, a new primary manager system is elected. The primary
manager system is the manager system with the most up-to-date configuration.
If a manager system rejoins the manager network or if a new manager system
is created and added to the manager network, that manager system receives
the latest configuration from the primary manager system.
For more information on creating manager systems, refer to Section 11.3.2,
“Adding a Manager System,” on page 11-9.