Managing Serviceguard Extension for SAP, December 2007

Understanding Serviceguard Extension for SAP
Dialog Instance Clusters as Simple Tool for Adaptive Enterprises
Chapter 1 29
The advantage of this setup is, that after repair of node1, the Dialog
Instance package can just be restarted on node1 instead of node2.This
saves downtime that would otherwise be necessary caused by a failback
of the dbciSID package. The two instances can be separated to different
machines without impacting the production environment negatively. It
should be noted that for this scenario with just two hosts there is no
requirement to enable automatic failover for the Dialog Instance package
Handling of Redundant Dialog Instances
Non-critical SAP Application Servers can be run on HP-UX, SUSE or
RedHat LINUX application server hosts. These hosts do not need to be
part of the Serviceguard cluster. Even if the additional SAP services are
run on nodes in the Serviceguard cluster, they are not necessarily
protected by Serviceguard packages. A combination of Windows/HP-UX
application servers is technically possible but additional software is
required to access HP-UX filesystems or HP-UX-like remote shells from
the Windows system.
Non-clustered SAP JAVA instances are not handled by SGeSAP. All
non-packaged ABAP instances are subsequently called Additional
Dialog Instances or sometimes synonymously Additional SAP
Application Servers to distinguish them from mission-critical Dialog
Instances. An additional Dialog Instance that runs on a cluster node is
called an Internal Dialog Instance. External Dialog Instances run on
HP-UX or Linux hosts that are not part of the cluster.
Even if Dialog Instances are external to the cluster, they may be affected
by package startup and shutdown. For convenience, non-critical ABAP
Dialog Instances can be started and stopped with any SGeSAP package
that secures critical components. Some SAP applications require the
whole set of Dialog Instances to be restarted during failover of the
Central Instance package. This can also be done with SGeSAP means.
Dialog Instances can be marked to be of minor importance. They will
then be shut down, if a critical component fails over to the host they run
on in order to free up resources for the non-redundant packaged
components.
Additional Dialog Instances never get reflected in package names.