Dedicated NFS Packages

packages. Otherwise, situations can arise in which a failover of the combined ASCS/SCS package is not possible. Finally, ASCS can not be combined with its ERS instance (AREP) in the same package. For the same reason, SCS can not 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 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.

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 SAPDB executable directory. The SAPDB client libraries are part of the global SAPDB executable directory and access to these files is needed by APO and liveCache at the same time.

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, this allows to avoid additional SPOFs in Dialog Instances. 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'.

Dialog Instance packages allow an uncomplicated approach to achieve abstraction from the hardware layer. It is possible to shift around Dialog Instance packages between servers at any given time. This might be desirable if the CPU resource consumption is eventually balanced poorly due to changed usage patterns. Dialog Instances can then be moved between the different hosts to address this. A Dialog Instance can also be moved to a standby host to allow planned hardware maintenance for the node it was running on.

One can simulate this flexibility by installing Dialog Instances on every host and activating them if required. This might be a feasible approach for many purposes and saves the need to maintain virtual IP addresses for each Dialog Instance. But there are ways that SAP users unintentionally create additional short-term SPOFs during operation if they reference a specific instance via its hostname. This could e.g. be done during batch scheduling. With Dialog Instance packages, the system becomes invulnerable against this type of user error.

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