Oracle Real Application Clusters

1.Overview
2.Benefits of using RAC

1.Overview
Oracle Real Application Clusters (Oracle RAC) enables a single database to run across a group of servers, providing fault tolerance, performance, and scalability with no application changes necessary. Oracle RAC provides high availability for applications by removing the single point of failure with a single server.
In a standard Oracle configuration, a database can only be mounted by one instance but in a RAC environment many instances can access a single database.

2.Benefits of using RAC
Running Oracle in RAC mode can benefit you in the following ways:
1. High availability
If some nodes fail, the remainder of the nodes will still be available for processing requests. Failover support is available from Oracle 8 with Oracle's Transparent Application Failover (TAF) technology and from Oracle 10g, server side load balancing.

2. Speedup (increased transaction response time)
RAC normally adds some overhead. However, for some DSS applications one can achieve increased performance by running operations in parallel (mainly for DSS applications).

3. Scalability (increased transaction volume)
RAC can be used to provide increased application scalability (mainly used for OLTP applications).