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

NOTE:
• Module-based SGeSAP database packages cannot be combined with a legacy based NFS
toolkit to create a single package.
• The major advantage of this approach is, that the failed SAP package will never cause a
costly failover of the underlying database since it is separated in a different package.
• It is not a requirement to do so, but it can help to reduce the complexity of a cluster setup,
if SCS and ASCS are combined in a single package. Under these circumstances, it needs to
be considered that the failure of one of the two instances will also cause failover for the other
instance. This might be tolerable in those cases in which SAP replication instances are
configured (see below).
The process of failover results in downtime that typically lasts a few minutes, depending on the
work in progress when the failover takes place. A main portion of downtime is needed for the
recovery of a database. The total recovery time of a failed database can not be predicted reliably.
By tuning the Serviceguard heartbeat on a dedicated heartbeat LAN, it is possible to achieve
failover times in the range of about a minute or two for a ci package that contains a lightweight
[A]SCS instance without database.
NOTE: sgesap/sapinstance packages can identify the state of a corresponding
sgesap/dbinstance package in the same cluster without the requirement of explicitly
configuring Serviceguard package dependencies. The information is for example used to delay
SAP instance package startups while the database is starting in a separate package, but not yet
ready to accept connections.
A cluster can be configured in a way that two nodes back up each other. The principle layout is
depicted in figure 1-1. This picture as well as the following drawings are meant to illustrate basic
principles in a clear and simple fashion. They omit other aspects and the level of detail that would
be required for a reasonable and complete high availability configuration.
Figure 1-1 Two-Package Failover with Mutual Backup Scenario
14 Designing SGeSAP Cluster Scenarios