Veritas Storage Foundation 5.0 for Oracle RAC Configuration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Introducing Serviceguard Extension for RAC
How Serviceguard Extension for RAC Works (High-Level Perspective)
Chapter 1
11
How Serviceguard Extension for RAC Works
(High-Level Perspective)
Real Application Clusters (RAC) is a parallel database environment that takes
advantage of the processing power of multiple computers. The Oracle database is the
physical data stored in tablespaces on disk, while the Oracle instance is a set of
processes and shared memory that provide access to the physical database. Specifically,
the instance involves server processes acting on behalf of clients to read data into shared
memory and make modifications to it, and background processes to write changed data
to disk.
In traditional environments, only one instance accesses a database at a specific time.
SGeRAC enables all nodes to concurrently run Oracle instances and execute
transactions against the same database. This software coordinates access to the shared
data for each node to provide consistency and integrity. Each node adds its processing
power to the cluster as a whole and can increase overall throughput or performance.
At a conceptual level, SGeRAC is a cluster that manages applications (instances),
networking, and storage components using resources contained in service groups.
SGeRAC clusters have many of the same properties as Serviceguard clusters:
• Each node runs its own operating system.
• A cluster interconnect enables cluster communications.
• A public network connects each node to a LAN for client access.
• Shared storage is accessible by each node that needs to run the application.
SGeRAC adds these technologies to a failover cluster environment, which are engineered
specifically to improve performance, availability, and manageability of Oracle RAC
environments:
• Cluster File System (CFS) and Cluster Volume Manager (CVM) technologies to
manage multi-instance database access to shared storage.
• An Oracle Disk Manager (ODM) library to maximize Oracle disk I/O performance.
• Interfaces to Oracle Clusterware (referred to as CRS—formerly Cluster Ready
Services) and RAC for managing cluster membership and communication.
SGeRAC provides an environment that can tolerate failures with minimal downtime and
interruption to users. If a node fails as clients access the same database on multiple
nodes, clients attached to the failed node can reconnect to a surviving node and resume
access. Recovery after failure in the SGeRAC environment is far quicker than recovery
for a failover database because another Oracle instance is already up and running. The
recovery process involves applying outstanding redo log entries from the failed node.
Refer to Using Serviceguard Extension for RAC and the Serviceguard Extension for RAC
Release Notes for additional information.