Components of high availability
High availability provides access to critical business applications and data in the event of a disruption in service. IBM® i high availability solutions minimize and sometimes eliminate the effect of planned and unplanned outages and site-wide disasters for your business. The basis for IBM i high availability solutions is cluster technology.
A cluster is two or more systems (or operating system images) that share resources and processing and provide backup in the event of an outage. With clustering, high availability is viewed not as a series of identical copies of the same resource across these systems but rather a set of shared resources that continually provide essential services to users and applications.
Clustering does not provide a complete high availability solution all by itself, but it is the key technology on which all IBM i high availability solutions are based. Clustering infrastructure, called cluster resource services, provides the underlying mechanisms for creating and managing multiple systems and their resources as one unified computing entity. Clustering also monitors systems and resources defined in the high availability environment for failures and responds accordingly, depending on the type of outage. Clustering combines hardware and software to reduce the cost and effect of planned and unplanned outages by quickly restoring services when these outages occur. Although not instantaneous, cluster recovery time is rapid.
The following section defines the key components of a high availability solution.
- Application resilience
Application resilience can be classified by the effect to the user. Under an IBM i clustering infrastructure, application resiliency is controlled with an application Cluster Resource Group object (CRG). This CRG provides the mechanism, using an exit program, to control start, stop, restart, and switch of the application to back up systems. The entire application environment, including data replication and switchable devices can be controlled through the clustering infrastructure as a single entity. - Levels of application resiliency
Application resiliency can be customized to the level of resiliency that your business requires using the features of the IBM i clustering framework. - Data resilience
You can use a number of technologies to address the data resilience requirements that are described in the “Benefits of High Availability” section. Following are the data resilience technologies. Keep in mind that multiple technologies can be used in combination to further strengthen your data resiliency. - Environment resilience
Environment resilience can be broken up into two sections, the physical environment, and the logical environment. The physical environment, which is really part of single system availability, focuses on things such as hardware redundancy, network topology, power infrastructure, and cooling capabilities. The logical environment is the application hosting and execution environment. It includes things like system settings, user profiles and system attributes that allow the user to run the application on multiple servers. - Simplicity
IBM i high availability addresses the three areas of customization, control, and automation with the goal of operational simplicity.
