Making Changes to Coupling Facility Devices and Control Units

Coupling facility devices and control units are defined to represent the connections in the channel subsystem connection to a coupling facility. The coupling facility control unit and device definitions are created in an IODF when you connect CF sender and CF receiver channel paths or two CF peer channel paths using HCD. One coupling facility control unit and two coupling facility devices are defined when you first connect a CF sender channel path to a CF receiver channel path for a coupling facility. Each subsequent channel connection adds two more coupling facility device definitions. For a CF peer channel connection, one control unit and seven CF device definitions are generated on one or on both sides of the connection depending on whether the sending function is used on only one or on both sides of the connection. You do not explicitly add or delete coupling facility devices and control units in the IODF; they are added and deleted based on the CF sender-to-receiver or peer-to-peer channel connections that you make.

A CF sender-to-CF receiver or peer-to-peer connection can cause changes to a coupling facility control unit definition. The first path you connect adds the coupling facility control unit and the last path you disconnect deletes the coupling facility control unit, but all other connections and disconnections of channel paths change the control unit definition.

The following sections describe how dynamic changes are made to coupling facility devices and control units when you connect and disconnect channel paths for a processor.