Managing Serviceguard Extension for SAP on Linux (IA64 Integrity and x86_64), February 2008

Understanding Serviceguard Extension for SAP on Linux
Designing Serviceguard Extension for SAP on Linux Cluster Scenarios
Chapter 1 13
Every ABAP Engine also requires a database service. Usually, this is
provided by ORACLE or MAXDB RDBMS systems. 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.
If you are planning a three-tier SAP layout, use the Serviceguard
Extension for SAP on Linux two-package model. The SAP WAS
functionality is separated into two Serviceguard Extension for SAP on
Linux packages, one for the database (db) and the other for the SAP WAS
Central Instance (ci). In small and medium size environments, the
database package gets combined with Highly Available NFS server
functionality to provide all file systems that are required by the software
in both packages.
There are some advantages to this approach. Usually a Central Instance
can reconnect to a failed database, once the database got restarted by
Serviceguard Extension for SAP on Linux on the failover node. A failed
Central Instance will never cause a failover of the underlying database if
it is separated in a different package.
The process of failover results in downtime that can last several 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 easily.
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.