High availability overview
The high availability concept defines a system that provides continuous operation and it makes sure that business and productivity continues during the possible downtimes. During these downtimes, the critical services and resources are accessed from a shared storage system.
The high availability clusters consist of multiple computers, called nodes, backing up the main server. They provide continuous usage of the system data. The high availability software monitors resources, such as disk drives, adapters, and network links. When a failure is detected, the high availability system automatically transfers the data to another system. A high availability solution is intended for mission-critical database and transaction-processing applications by eliminating single points of failure (SPOF) in your installation through appropriate design, planning, hardware selection, software configuration, and carefully controlled change management processes. The high availability solution has two of everything. If any component should fail, a redundant backup component is waiting to take over the workload.
A common configuration for the high availability systems consists of a two-node cluster. This is a basic and minimum setup of the system but more nodes can be added to ensure greater continuity in case of a server failure.
The cluster is defined as loosely coupled machines working together. Each cluster is connected to a node which is a server running its own operating system. Each node must be configured to obtain the data from another node that is down.