You can combine up to three application servers to form a cluster and add a fourth server for redundancy as long as the active traffic does not exceed 300 ports. Each cluster supports flexible, per user message stores. The message store can be the Avaya storage server, a Microsoft Exchange server, or a VMware Zimbra server.
Using clustering application servers, you can increase the system capacity to support more users. Every application server increases the number of available ports.
Clustering also provides redundancy for all application servers in a cluster because all application servers within a cluster are configured identically and are therefore interchangeable.
Clustering handles data as follows:
User passwords and greetings are replicated on each clustered application server.
Messages are distributed among the clustered servers.
The global address list (GAL) and personal user lists are synchronized on each application server during the nightly maintenance.