Managing Serviceguard Extension for SAP Version B.05.10, September 2010

Configuring the Update Service as part of the packaged Central Instance is recommended.
Consider using local update servers only if performance issues require it. In this case, configure
Update Services for application services running on the same node. This ensures that the remaining
SAP Instances on different nodes are not affected if an outage occurs on the Update Server.
Otherwise, a failure of the Update Service will lead to subsequent outages at different Dialog
Instance nodes.
Dedicated Failover Host
More complicated clusters that consolidate a couple of SAP applications often have a dedicated
failover server. While each SAP application has its own set of primary nodes, there is no need
to also provide a failover node for each of these servers. Instead, there is one commonly shared
secondary node that is in principle capable to replace any single failed primary node. Often,
some or all of the primary nodes are partitions of a large server.
Figure 1-5 Replicated Enqueue Clustering for ABAP and JAVA Instances
Figure 1-5 shows an example configuration. The dedicated failover host can serve many purposes
during normal operation. With the introduction of Replicated Enqueue Servers, it is a good
practice to consolidate a number of Replicated Enqueues on the dedicated failover host.
These replication units can be halted at any time without disrupting ongoing transactions for
the systems they belong to. They are sacrificed in emergency conditions when a failing database
and/or Central Service Instance need the spare resources.
Dedicated Failover Host 21