Distributing workloads
The ability to route a request to any server in a group of clustered appservers allows servers to share work and improve throughput of client requests. Requests can be evenly distributed to servers to prevent workload imbalances in which one or more servers has idle or low activity while others are overburdened. This load balancing activity is a benefit of workload management.
Thus, the proposed configuration should ensure that each LPAR or server in the configuration processes a fair share of the overall client load that is being processed by the system as a whole. In other words, it is not efficient to have one LPAR overloaded while another LPAR is mostly idle. If all LPARs have roughly the same capacity (for example, CPU power), then each LPAR should process a roughly equal share of the load. Otherwise, there likely needs to be a provision for workload to be distributed in proportion to the processing power available on each LPAR.
Using weighted definitions of cluster members allows nodes (or LPARs) to have different hardware resources and still participate in a cluster. The weight specifies that the appserver with a higher weight will be more likely to serve the request faster, and workload management will consequently send more requests to that node.
With several cluster members available to handle requests, it is more likely that failures will not negatively affect throughput and reliability. With cluster members distributed to various nodes, an entire machine can fail without any application downtime. Requests can be routed to other nodes if one node fails. Clustering also allows for maintenance of nodes without stopping application functionality.
To read detailed descriptions of workload management policies, and learn how requests are distributed among available servers, refer to Chapter 6 and to Chapter 7 of WebSphere Application Server V6 Scalability and Performance Handbook, SG24-6392.