Compaq ProLiant 6500 Compaq Parallel Database Cluster Model PDC/O1000 for Orac - Page 22
Availability, The PDC/O1000 uses non-redundant Fibre Channel Fabric Storage Area
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Clustering Overview 1-3 The PDC/O1000 uses non-redundant Fibre Channel Fabric Storage Area Network (SAN) and non-redundant Fibre Channel Arbitrated Loop (FC-AL) SAN topologies for its shared storage I/O data paths. These two SAN topologies support the use of multiple non-redundant fabrics and loops, respectively. In the example shown in Figure 1-1, the clustered nodes are connected to the database on the shared storage subsystems through a non-redundant Fibre Channel Fabric or non-redundant FC-AL. Clients access the database through the client LAN, and the cluster nodes communicate across an Ethernet cluster interconnect. 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, the operating system, and the 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 a 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 distribute 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.