When you enable a Metadata Access Service that runs on a single node, a service process starts on the node.
Primary and back-up nodes
When you enable a Metadata Access Service configured to run on primary and back-up nodes, a service process is available to run on each node, but only the service process on the primary node starts. For example, you have the high availability option and you configure a Metadata Access Service to run on a primary node and two back-up nodes. You enable the Metadata Access Service, which enables a service process on each of the three nodes. A single process runs on the primary node, and the other processes on the back-up nodes maintain standby status.