The simplest Messaging implementation is the single server, single site configuration, in which the application role and the storage role are performed by a single virtual machine within System Platform. The single server configuration is an ideal solution for organizations up to a maximum of 5,500 users.
A benefit of this configuration is that if you have fewer than the maximum number of users at your main site, you can add additional application servers at remote office locations. With this scalability, you can easily expand your single server configuration to other Messaging configurations. For example, you might have 2,000 users at your main site and several remote locations with a few hundred users each. In this case, you can add remote users either by placing application servers at those locations or by servicing those users at other sites over WAN, up to the maximum 5,500 users. For this reason, the single server configuration works well for small or distributed organizations and can accommodate such organizations as the organizations grow.
A restriction applies, however. You can add application servers to a single server configuration. But you cannot configure application servers into a cluster with the application role that is on the single server. To expand your single server system into a system with clustered application servers, you must first put the application and storage roles on to dedicated servers. Then you can add other application servers as needed. You cannot use a single-server configuration with a third-party storage server. For more information on server requirements, see Message store.
Note An application server can support only one site.
