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A typical RAC implementation groups multiple Oracle database instances running on multiple machines (or nodes). These nodes communicate with each other and share a common pool of disks. The disks house all of the data files that comprise the database. This architecture is illustrated in Figure 9-9.
Let's look at a few of the key components in Figure 9-9:
Each node is connected to each other using high bandwidth communications.
Each node has its own set of log (redo) files.
The Cluster Manager monitors the status of each database instance in the cluster and enables communication between the instances. This manager is known as the Cluster Synchronization Services (CSS). In previous versions of Oracle, it was just referred to as the ''Cluster Manager." When RAC was first introduced, cluster management was performed by third-party software, which is still supported by Oracle Database 10g.
FIGURE 9-7. Real Application Clusters—conceptual architecture
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