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

About Three-Tier Configurations
A three-tier client server configuration consists of database (Database Layer) on a machine, and some or all
of the SAP applications (SAP Application Layer) running on one or more different machines.
Figure 1-3 Three-Tier Client Configuration
Benefits of a Three-Tier Configuration:
1. Making the SAP system more efficient by off-loading CPU intensive SAP processes to one or more
machines.
2. Reduce failover times. When a failure occurs, typically, the majority of the downtime is needed to
recover the database. Although the total recovery time of a failed database cannot be predicted, failover
times can be reduced when the Central Instance and the database are on different machines.
• In the case of a database failure, the Database Serviceguard package will failover to another
cluster node, independent of any SAP component.
• In the case of a Central Instance failure, it can be configured to automatically reconnect to a
previously failed database, once the database has been restarted by Serviceguard Extension for
SAP on Linux on the failover node.
3. When the database and Central Instance are on different machines, a failed Central Instance will not
cause a failover of the database.
4. If the CI instance requires even additional off-loading, the Dual Stack Configuration example in the
next section shows how the CI can be separated.
18 Understanding Serviceguard Extension for SAP on Linux