READ ME before using the Veritas Storage Foundation™ 5.1 SP1 for Oracle RAC Administrator's Guide (April 2011)

• Increase availability and performance with dynamic multipathing (DMP), which provides wide
storage array support for protection from failures and performance bottlenecks in the HBAs
and SAN switches.
• Optimize I/O performance through storage mapping technologies and tunable attributes.
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.
8 Introducing Serviceguard Extension for RAC