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Oracle RAC, introduced with Oracle9i, is the successor to Oracle Parallel Server (OPS). RAC allows multiple instances to access the same database (storage) simultaneously. It provides fault tolerance, load balancing, and performance benefits by allowing the system to scale out, and at the same time because all nodes access the same database the failure of one instance will not cause the loss of access to the database. At the heart of Oracle RAC is a shared disk subsystem. All nodes in the cluster must be able to access all of the data, redo log files, control files and parameter files for all nodes in the cluster. The data disks must be globally available to allow all nodes to access the database. Each node has its own redo log and control files but the other nodes must be able to access them in order to recover that node in the event of a system failure. |
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