A cluster node is a Microsoft® Windows NT® Server system that has a working installation of Microsoft® Cluster Server. A node can be an active or inactive member of a cluster, depending on whether or not it is currently online and in communication with the other cluster nodes. An active node can act as host to one or more cluster groups.
When an administrator installs Cluster Server, a choice must be made as to whether the system should form its own cluster or join an existing cluster. After installation is complete, the node will always attempt to join an existing cluster whenever it is restarted. To join the existing cluster, Cluster Server validates the node's name, password, and cluster database. Active membership is restored if the name and password are valid and consistency exists between this cluster database and the cluster databases residing on the other nodes in the cluster.
If a node cannot join an existing cluster because it cannot locate another active node, it attempts to form its own cluster by gaining access to the quorum resource. The quorum resource is the resource, typically a disk, that stores the cluster's recovery logs. The recovery logs are used by the Cluster Service to keep the cluster databases residing on each cluster node consistent. If access is granted, the node verifies whether or not its cluster database has the same information as the recovery logs. After the cluster database and recovery logs are synchronized, a new cluster is able to form.