General Requirements

Both topologies must meet the following general requirements:

• Machines that host HADB nodes must be in pairs. That is, there must be an even number of them.

• Each data redundancy unit (DRU) must have the same number of machines. Create the HADB database in such a way that the mirrored (paired) nodes are on a different DRU than the primary nodes.

• Each machine that hosts HADB nodes must have local disk storage, used to store all persisted information in the HADB.

• Machines that host the HADB nodes must run the same operating system. It is best to use identical or nearly identical machines, in terms of configuration and performance.

• For HTTP and SFSB session information to be persisted to the HADB, the Application Server instances must be in a cluster and satisfy all related requirements. For more information on configuring clusters, see Chapter 5, Using Application Server Clusters, in Sun Java System Application Server 9.1 High Availability Administration Guide.

• Machines hosting the Application Server instances must be as identical as possible, in terms of configuration and performance. This is because the load balancer plug-in uses a round-robin policy for load balancing, and if machines of different classes host instances, then the load will not be balanced in the most optimum way across these machines.

• Preferably have a separate uninterruptible power supply (UPS) for each DRU.