Managing Serviceguard Extension for SAP Version B.05.10, December 2012

(and similarly the legacy package type db) clusters any of these databases. The module unifies
the configuration, so that database package administration for all database vendors is treated
identically. sgesap/dbinstance can be used with any type of SAP application, independent
of whether it is ABAP-based or JAVA-based or both. In case they are available, the module will
take advantage of database tools that are shipped with certain SAP applications.
A SGeSAP legacy jdb package contains a database instance for SAP JAVA applications. A
SGeSAP legacy db package contains a database instance for an ABAP application or a combined
ABAP and JAVA application.
If you are planning a simple three-tier SAP layout in a two node cluster, use the SGeSAP mutual
failover model. This approach distinguishes two SGeSAP packages—one for the database SPOF
and the other for the SAP SPOFs as defined above. In small and medium size environments, the
database package gets combined with HA NFS server functionality to provide all filesystems that
are required by the software in both packages. During normal operation, the two packages are
running on different nodes of the cluster. The major advantage of this approach is that the failed
SAP package will never cause a costly failover of the underlying database because it is separated
in a different package.
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.
A cluster can be configured in a way that two nodes back up each other. The basic layout is
depicted in figure 1.
Figure 1 Two-Package Failover with Mutual Backup Scenario
It is a best practice to base the package naming on the SAP instance naming conventions whenever
possible. Each package name should also include the SAP System Identifier (SID) of the system to
which the package belongs. If similar packages of the same type get added later, they have a
distinct namespace because they have a different SID.
Mutual Failover Scenarios Using the Two Package Concept 11