A cluster is a group of nodes working together as single systems, to ensure high availability of applications. Avidware deals with Exchange Server 2003, and clustering to ensure higher availability than on a stand-alone server. Now the key thing to keep in mind here is that this is primarily hardware redundancy and not data redundancy; there is no data replication. That would all depend on the physical hardware such as disk arrays. As you see here, we have two cluster nodes standing by the pink computers, and in between we have two shared disks, and those are your physical disks.

We also handle virtual servers. A virtual server is nothing more than a group that is inside of a cluster. It needs a minimum of four cluster resources. We have an IP address, a network name, a physical disk, and an application. In this case, the application is Exchange. When we have Exchange as that application, we refer to it as an EVS or an Exchange Virtual Server.