For multiple system environments, you can use clusters as a strategy to maintain a high or continuous availability for your systems and applications.
A cluster is a collection or group of multiple systems that work together as a single server. If your business needs high or continuous availability, clustering is the solution that you should consider.
Systems in a cluster work cooperatively to provide a single computing solution. You can have up to 128 systems in a cluster. This allows you to efficiently group your systems together to set up an environment that provides availability that approaches 100 percent for your critical applications and data. This helps ensure that your essential systems and applications are always available. Clusters also provide simplified systems management and increased scalability to seamlessly add new components as your business grows.
You have to weigh the cost of this solution against the cost of downtime on your system to decide whether to implement clusters in your business.
If you do choose to use clusters in your environment, you will have the added benefit of improving application availability. The level of application availability will depend on how well the application integrates with cluster resource services. For more information on these applications, see Highly available programs.
To learn more about clusters, including how it works and how to implement
clusters in your business, see Clusters.
For more information on clusters in the context of other high availability
solutions, see High availability and clusters 
.
Highly available programs
Highly available applications provide users continued access to data and application functions despite planned or unplanned outages. i5/OS™ has provided an application resilience architecture that supports various degrees of highly available application. Applications at the high end of the availability spectrum are enhanced with integrated functions and provide automation of the environment. These functions are controlled by cluster management utilities. For more information on these topics, see Cluster applications.
iSeries™ cluster middleware
iSeries cluster middleware is a group of competitive third party products which provide cluster management and data replication functions and services. These products make full use of the Cluster Resource Services functions of i5/OS and adhere to the iSeries cluster architecture. For a list of cluster middleware and a description of the criteria these programs must meet, see High Availability and Clusters.