Compaq ProLiant 6500 Compaq Parallel Database Cluster Model PDC/05000 for Orac - Page 23

1-4 Compaq Parallel Database Cluster Model PDC/O5000 for Oracle8i and Windows 2000 Administrator Guide Availability When computer systems experience outages, the amount of time the system is unavailable is referred to as downtime. Downtime has several primary causes: hardware faults, software faults, planned service, operator error, and environmental factors. Minimizing downtime is a primary goal of a cluster. Simply defined, availability is the measure of how well a computer system can continuously deliver services to clients. Availability is a system-wide endeavor. The hardware, operating system, and applications must be designed for availability. Clustering requires stability in these components, then couples them in such a way that failure of one item does not render the system unusable. By using redundant components and mechanisms that detect and recover from faults, clusters can greatly increase the availability of applications critical to business operations. Scalability Simply defined, scalability is a computer system characteristic that enables improved performance or throughput when supplementary hardware resources are added. Scalable systems allow increased throughput by adding components to an existing system without the expense of adding an entire new system. In a stand-alone server configuration, scalable systems allow increased throughput by adding processors or more memory. In a cluster configuration, this result is usually obtained by adding cluster nodes. Not only must the hardware benefit from additional components, but also software must be constructed in such a way as to take advantage of the additional processing power. Oracle8i Parallel Server distributes the workload among the cluster nodes. As more nodes are added to the cluster, cluster-aware applications can use the parallel features of Oracle8i Parallel Server to distribute workload among more servers, thereby obtaining greater throughput.