An Enterprise Vault cluster consists of:

• One or more primary nodes, each normally hosting an Enterprise Vault virtual server.

• One or more failover nodes: standbys that can take over the job of hosting an Enterprise Vault virtual server if a primary node fails.

Enterprise Vault does not permit "active/active" cluster configurations. That is, only one Enterprise Vault virtual server can run on a clustered node at any one time. You can configure Enterprise Vault in any operation mode that adheres to this restriction, such as:

• An active/passive failover pair: a primary node with a dedicated failover node.

• N+1 (hot standby server): two or more primary nodes share a single failover node. Only one node failure can be accommodated at any one time.

• N+M: an extension of the hot standby concept with N primary nodes and M failover nodes. Only M node failures can be accommodated at one time.

• N+M 'any-to-any': identical to N+M, except that there is no need to fail back to the original node after a failover. When the original node becomes available again, it can operate as a failover node.