Using Serviceguard Extension for RAC, 6th Edition, April 2008

Figure 1-1 Overview of Oracle RAC Configuration on HP-UX
In the figure, two loosely coupled systems (each one known as a node) are running
separate instances of Oracle software that read data from and write data to a shared
set of disks. Clients connect to one node or the other via LAN.
RAC on HP-UX lets you maintain a single database image that is accessed by the HP
servers in parallel, thereby gaining added processing power without the need to
administer separate 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
22 Introduction to Serviceguard Extension for RAC