Defining coupling facility components in a sysplex

A coupling facility is a special logical partition that runs the coupling facility control code (CFCC) and provides high-speed caching, list processing, and locking functions in a sysplex. HCD enables you to specify whether a logical partition can be a coupling facility, operating system, or either on certain processors. You connect the coupling facility logical partition to a processor through the coupling facility channels as shown in Figure 1.

Figure 1. Example of a Sysplex
Example of a Sysplex

Processors of different types provide support of coupling facility (CF) channel paths of different types. For the list of CF path types supported by your processor, see "Machine limits and rules" in the IOCP User's Guide.

Using HCD, you define:
  • A logical partition in which the coupling facility runs.
  • Coupling facility (CF) sender channel paths and CF receiver channel paths or coupling facility (CF) peer channel paths. You define a coupling facility sender channel path to a logical partition running an operating system or a processor in basic mode running an operating system. You define a coupling facility receiver channel path to a logical partition running a coupling facility. On an IBM® zSeries 890 or later processor, you define CF peer channels on both sides of a coupling facility connection. A CF peer channel contains both sender and receiver functions. However, it is not required that these functions are used on both sides.
    Note: With CF Duplexing, a CF logical partition can use the coupling facility sender function to communicate with another CF logical partition. As a result, you can define sender channel paths besides the receiver channel paths in a CF partition.
  • Coupling facility control unit and devices. When you connect CF sender and CF receiver channel paths, or CF peer channel paths, HCD proposes coupling facility control unit and device numbers that must be defined for a CF sender channel. (CF receiver channels do not require control units and devices to be defined.) When you connect two CF peer channel paths, HCD proposes coupling facility control unit and device numbers on one or both sides of the connection depending on whether the sending function is used on only one or on both sides. You can override HCD's proposal to specify your own numbers for the control unit and device definitions.

    These coupling facility control units and devices have different characteristics than control units and devices. The ones defined as a result of coupling facility connections are referred to as coupling facility control units and coupling facility devices.

    Regardless of the CF channel path type used for the coupling facility connection, HCD uses:
    • Control unit type CFS and the device type CFS for the generated CF control units and CF devices specified for a CF sender channel path
    • Control unit type CFP and device type CFP for the generated control units and CF devices specified for each of the CF peer channel paths

When you make connections between coupling facility channel paths, a coupling facility control unit and coupling facility devices are defined to represent the connections in the channel subsystem connection to the coupling facility. Actual number of coupling facility devices defined for each coupling facility path connection depends on a type of CF channel path involved. HCD does not create coupling facility devices for connected coupling facility channel paths defined as STP-only. One coupling facility control unit is defined for each coupling facility that a processor connects to. For example, one control unit is defined when two logical partitions on a processor are connected to the same coupling facility partition.

Coupling facility control units and devices are automatically defined by the CF sender-to-receiver or peer-to-peer connections that are established. You do not have to use the Define Control Unit Data option that you use to define control units and you do not have to use the Define Device Data option that you use to define I/O devices. See Making changes to coupling facility devices and control units for information about changes to the coupling facility definitions.

The characteristics that distinguish coupling facility components are:
  • UIMs are not needed for coupling facility devices
  • Coupling facility devices are not represented by UCBs
  • An EDT and dynamic allocation do not pertain to coupling facility devices
  • You do not select a preferred channel path to a coupling facility device
  • You do not vary coupling facility devices offline
  • Channel measurement blocks (CMBs) do not apply to coupling facility devices
  • You cannot specify a unit address for a coupling facility device
  • The concept of logical versus physical control unit does not apply
  • You cannot specify a logical address for a coupling facility control unit.

To allow an operating system image to communicate with a coupling facility image in the same CPC without requiring any hardware resources, you can use Internal Coupling (IC) channels. Coupling communication over IC channel paths is provided by the CP microcode. Coupling channels can be configured into image along with Internal Coupling (IC) channels that need to be defined.

Except for channel packaging and providing connection information, IC channels follow the same configuration rules as real coupling facility channels.

Because you need no real hardware to perform IC functions, define IC channels with CHPID numbers that are not installed or are unusable because of other installed hardware. For the same reason, IC channels are defined without PCHIDs. An attempt to add a PCHID to an IC definition results in message CBDG523I.

Define the IC channels with the following types:
  • CF sender channel with type ICS
  • CF receiver channel with type ICR
  • CF peer channel with type ICP.