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

instances. It is also supported to combine the replication instances within one SGeSAP package.
It is also supported to combine ASCS and SCS in one package, but only if the two ERS instances
are likewise combined in another package. It is not supported to combine ASCS and SCS in one
package and keep the two ERS instances in two separate packages. Otherwise, situations can
arise in which a failover of the combined ASCS/SCS package is not possible. Finally, ASCS cannot
be combined with its ERS instance (AREP) in the same package. For the same reason, SCS cannot
be combined with its ERS instance (REP).
The sgesap/sapinstance module can be used to cluster Enqueue Replication Instances.
Furthermore, SGeSAP offers the legacy package types rep and arep to implement enqueue
replication packages for JAVA and ABAP.
SAP offers two possibilities to configure Enqueue Replication Servers:
1. SAP self-controlled using High Availability polling.
2. Completely High Availability failover solution controlled.
SGeSAP provides a completely High Availability failover solution and controlled implementation
that avoids costly polling data exchange between SAP and the High Availability cluster software.
There are several SAP profile parameters that are related to the self-controlled approach. Most
of these parameters have names that start with the string enque/enrep/hafunc_. They will
not have any effect in SGeSAP clusters.
Dedicated NFS Packages
Small clusters with only a few SGeSAP packages usually provide HA NFS by combining the HA
NFS toolkit package functionality with the SGeSAP packages that contain a database component.
The HA NFS toolkit is a separate product with a set of configuration and control files that must
be customized for the SGeSAP environment. It needs to be obtained separately.
HA NFS is delivered in a distributed fashion with each database package serving its own
filesystems. By consolidating this into one package, all NFS serving capabilities can be removed
from the database packages. In complex, consolidated environments with several SGeSAP
packages, it is of significant help to use one dedicates HA NFS package instead of blending this
into existing packages.
A dedicated SAPNFS package is specialized to provide access to shared filesystems that are
needed by more than one mySAP component. Typical filesystems served by SAPNFS would be
the common SAP transport directory or the global MAXDB executable directory of MAXDB 7.7.
The MAXDB client libraries are part of the global MAXDB executable directory and access to these
files is needed by APO and liveCache at the same time. Beginning with MAXDB 7.8 isolated
installations, each database installation keeps a separate client.
SGeSAP setups are designed to avoid HA NFS shared filesystems with heavy traffic if possible.
For many implementations, this gives the option to use one SAPNFS package for all HA NFS
needs in the SAP consolidation cluster without the risk to create a serious performance bottleneck.
HA NFS might still be required in configurations that use Cluster File Systems in order to provide
access to the SAP transport directories to SAP instances that run on hosts outside of the cluster.
Dialog Instance Clusters as Simple Tool for Adaptive Enterprises
Databases and Central Instances are Single Points of Failure. ABAP and JAVA Dialog Instances
can be installed in a redundant fashion. In theory, additional SPOFs in Dialog Instances are
avoided. This doesn't mean that it is impossible to configure the systems including SPOFs on
Dialog Instances. A simple example for the need of a SAP Application Server package is to protect
dedicated batch servers against hardware failures.
Any number of SAP Application Server instances can be added to a package that uses the module
sgesap/sapinstance. SAP ABAP Dialog Instances can also be packages in SGeSAP legacy
package type 'd'. SAP JAVA Dialog Instances can be packaged using SGeSAP legacy package
type 'jd'.
18 Designing SGeSAP Cluster Scenarios