Availability; Scalability - Compaq 112726-001 - ProLiant - 6500 Administrator's Manual

1-4 Compaq Parallel Database Cluster Model PDC/O5000 for Oracle8i and Windows 2000 Administrator Guide

Availability

Scalability

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.
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.