Using Serviceguard Extension for RAC, 9th Edition, September 2010

databases. Further, when properly configured, Serviceguard Extension for RAC provides a highly
available database that continues to operate even if one hardware component should fail.
Group Membership
Oracle RAC systems implement the concept of group membership, which allows multiple
instances of RAC to run on each node. Related processes are configured into groups. Groups
allow processes in different instances to choose which other processes to interact with. This
allows the support of multiple databases within one RAC cluster.
A Group Membership Service (GMS) component provides a process monitoring facility to monitor
group membership status. GMS is provided by the cmgmsd daemon, which is an HP component
installed with Serviceguard Extension for RAC.
Figure 1-2 shows how group membership works. Nodes 1 through 4 of the cluster share the Sales
database, but only Nodes 3 and 4 share the HR database. Consequently, there is one instance of
RAC each on Node 1 and Node 2, and there are two instances of RAC each on Node 3 and Node
4. The RAC processes accessing the Sales database constitute one group, and the RAC processes
accessing the HR database constitute another group.
Figure 1-2 Group Membership Services
Using Packages in a Cluster
To make other important applications highly available (in addition to the Oracle Real Application
Cluster), you can configure your RAC cluster to use packages. Packages group applications and
services together. In the event of a service, node, or network failure, Serviceguard Extension for
RAC can automatically transfer control of all system resources in a designated package to another
node within the cluster, allowing your applications to remain available with minimal interruption.
There are failover packages, system multi-node packages, and multi-node packages:
The typical high-availability package is a failover package. It usually is configured to run on
several nodes in the cluster, and runs on one at a time. If a service, node, network, or other
package resource fails on the node where it is running, Serviceguard can automatically transfer
control of the package to another cluster node, allowing services to remain available with minimal
interruption.
16 Introduction to Serviceguard Extension for RAC