A cluster consists of two or more independent, but interconnected, servers. Several hardware vendors have
provided cluster capability over the years to meet a variety of needs. Some clusters were intended only to provide high availability by allowing work to be transferred to a secondary node if the active node fails. Others were designed to provide scalability by allowing user connections or work to be distributed across the nodes.
Another common feature of a cluster is that it should appear to an application as if it were a single server. Similarly, management of several servers should be as similar to the management of a single server as possible. The cluster management software provides this transparency.
For the nodes to act as if they were a single server, files must be stored in such a way that they can be found by the specific node that needs them. There are several different cluster topologies that address the data access issue, each dependent on the primary goals of the cluster designer.
The interconnect is a physical network used as a means of communication between each node of the cluster. In short, a cluster is a group of independent servers that cooperate as a single system.
Note: The clusters you are going to manipulate in this course all have the same operating system. This is a requirement for RAC clusters.
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