Clustering is architected to help facilitate continuous availability. Whether you experience a system outage, a site loss, or need planned downtime for system maintenance, access to the functions provided on a clustered system can be switched over to one or more other systems that contain a current copy of the critical application data.
The fundamental concept of clustering is that of resilient resources -- data, processes, applications, and devices that can be recovered if the system on which they exist fails. With clustering, resources are located on more than one system. If the system which is the primary access point for a particular set of resilient resources should fail, a pre-defined backup system becomes the primary access point.
IBM i clustering is designed so that each of the necessary components can work together to provide continuous availability for data and applications. The primary components of clustering, shown in Figure 1, are:
-
Cluster framework - functions and programming interfaces provided by IBM i and additional licensed programs
-
Resilient applications - software that is made resilient through exit programs which enable it to be controlled in a clustering environment, created with assistance from a high availability business partner (HABP)
-
Resilient data - middleware software for a variety of high availability technologies and the exit programs which enable it to be controlled in a clustering environment, provided by Precisely or IBM
-
Cluster management - tools and user interfaces provided by IBM and by Precisely
Figure 1.Components of a IBM i cluster solution
