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Donald K. Burleson

Oracle RAC Tips

Server Redundancy

The database resides within a server. The server or host is an important component in the provision of the data service. Any failure in the host system causes the database to go down.

Necessity of Server Redundancy

Clustered servers utilize two or more nodes, essentially keeping the extra nodes as standby or sometimes as extra computing power, as in the case of the RAC system. With the help of the additional nodes, we ensure that the standby node can provide the same database service to the user community. However, when in standby, it loses the performance and scalability level for which it is intended.

Clustering servers assures the administrators and the application users that at least one node is alive. A cluster, in its most general form, comprises two or more interconnected computers that are viewed and used as a single, unified computing resource. By using multiple systems, the impact of the failure of any individual system is kept low by passing the failed system’s workload to the remaining members of the cluster.

The standby node becomes functional, or becomes the primary host, when the failed host is unable to provide any host services. When some of the internal components fail and the failure is non-recoverable without intervention, the server is declared not available or simply ‘failed’. This indicates that there is a lot of scope for keeping the internal components safe or redundant.

Before losing the server and resorting to the use of the clustered backup node, there are many things we can do to keep the components from failing. Let us examine these methods that act as the first level of redundancy. Some people call it ‘high availability without clustering.’ In contrast to clustering, system availability can be improved without adding additional servers.

Redundancy Features

There are many features or options that add value to the redundancy at the server level. Taking advantage of such features helps avoid failures and avoids degraded cluster performance in systems like the RAC system. These features address different subsystems of the server, such as the memory and processors. Redundant components such as fans, power supplies, and adapters can also provide higher availability, particularly when used with software that provides monitoring and alerting capability to the system administrators.

To make the servers more reliable, we should use high-reliability components and best-system practices. Let us examine some features of the redundancy that administrators need to focus on.

For more information, see the book Oracle 11g Grid and Real Application Clusters 30% off if you buy it directly from Rampant TechPress . 

Written by top Oracle experts, this RAC book has a complete online code depot with ready to use RAC scripts.





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