Managing Serviceguard Extension for SAP on Linux (IA64 Integrity and x86_64), April 2009

the pointed brackets < > indicate the characters enclosed within are to be replaced by an installation specific
SID. The <INR> contains the installation number of a dialog instance.
• Two Package Concept for a database and ABAP instance: db<SID>, ci<SID>
• Two Package Concept for a database and JAVA instance: db<SID>, jci<SID>
• One Package Concept for a database and ABAP instance: dbci<SID>
• One Package Concept for a database and JAVA instance: dbjci<SID>
• Dialog instance: d<INR><SID>
• ABAP System Central Services: ascs<SID>
• JAVA System Central Services: scs<SID>
• The ABAP and JAVA Replicated Enqueue: ers<INR><SID>
• Dedicated NFS Packages: sapnfs
Failover Scenarios Using One and Two Package Concepts
SAP ABAP Engine or JAVA engine based applications usually rely on two central software services that
define the software SPOFs: the SAP Enqueue Service and the SAP Message Service. These services are
traditionally combined and run as part of a unique SAP Instance that is called the Central Instance (ci).
As any other SAP instance, the Central Instance has an Instance Name. Traditionally it is called DVEBMGS.
Each letter represents a service that is delivered by the instance. The "E" and the "M" stand for the Enqueue
and Message Service that were identified as SPOFs in the system. Therefore, the most important package
type of Serviceguard Extension for SAP on Linux is the Central Instance package (ci).
All other SAP services can be installed redundantly within additional Application Server instances, sometimes
also called Dialog Instances.
As its naming convention suggests, DVEBMGS, Dialog, Verbucher (=German for update) Enqueue Batch
Message Server Gateway Spool) includes additional services within the Central Instance, than just those that
cause SPOFs.
NOTE: In an SAP system there can be more services/processes that are not reflected in the above naming
convention, including; CO: SAP collector daemon, SE: syslog send daemon and IG: Internet Graphics.
An undesirable result of this is, that a Central Instance is a complex software with a high resource demand.
Shutdown and startup of Central Instances is slower and more error-prone than they could be. Starting with
SAP Web Application Server 6.40 it is possible to isolate the SPOFs of the Central Instance in a separate
Instance that is then called the ABAP System Central Service Instance, in short ASCS. The installer for SAP
Web Application Server allows installing ASCS automatically. This installation procedure will then also
create a standard Dialog Instance that is called DVEBMGS for compatibility reasons. This kind of DVEBMGS
instance does not provide Enqueue Service or Message Services and is therefore not considered as a Central
Instance even though its name implies otherwise.
NOTE: A Serviceguard Extension for SAP on Linux (ci) package contains either a full DVEBMGS instance
or a lightweight ASCS instance. In any case, the Serviceguard Extension for SAP on Linux (ci) package
provides failover capabilities to SAP Enqueue Services and SAP Message Services.
Every SAP instance also requires a database service. With SGeSAP/LX either ORACLE or MaxDB RDBMS
systems are supported. The package type (db) clusters any type of these databases. It unifies the configuration,
so that database package administration for all vendors is treated identically.
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.
14 Understanding Serviceguard Extension for SAP on Linux