Coupling facility channels

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Coupling facility channels are channels that provide the connectivity for data sharing between a coupling facility and the CPCs or logical partitions (LPs) directly attached to it. IOCP provides controls for defining coupling facility channels. However, IBM® recommends that, when possible, you use the Hardware Configuration Definition (HCD) to define the coupling facility channel configuration to the I/O subsystem.

HCD provides controls for defining coupling facility channels. HCD also automatically generates the control unit and device definitions associated with coupling facility sender and peer channel paths.

Coupling facility channels:
  • Require a point-to-point connection (direct channel attach between a CPC or LP and a coupling facility).
  • Can connect a coupling facility to other LPs on the same CPC when a coupling facility is one of multiple LPs running on a single CPC. Use internal coupling channels for these connections. Internal Coupling channels can be used only to connect a coupling facility and LPs on the same CPC.
  • Can be redundantly configured (two or more coupling facility channels from each CPC involved in coupling facility data sharing) to enhance availability and avoid extended recovery time. This statement does not apply to Internal Coupling channels.
  • Require CFR or CBR channel path definition (coupling facility receiver channel capability) at the coupling facility end of a coupling facility channel connection with a CFS or CBS channel path definition (coupling facility sender channel capability) at the ESA end of a coupling facility channel connection. You must use coupling facility sender and receiver channels when connecting to a CPC or CF that does not support coupling facility peer channels (for example, a 9672).
  • Require CFP, CBP, ICP, CIB, CL5, CL6, or CS5 channel path definition (coupling facility peer channel capability) at the coupling facility and ESA ends of a coupling facility channel connection. Using coupling facility peer channels is the recommended way to connect to a CPC or CF that does support peer channels. Some CPCs that support peer channels do not support CIB channels. Some CPCs that support CIB channels do not support CL5 and CS5 channels. CFP, CBP, ICP, CL5, CL6, CS5, or CIB channel paths can be shared by many ESA LPs and only one coupling facility LP at the same time.
  • Require the following connections:
    • The CFS channel path must be connected to a CFR channel path.
    • The CBS channel path must be connected to a CBR channel path.
    • The CFP channel path must be connected to another CFP channel path.
    • The CBP channel path must be connected to another CBP channel path. ICB-3 and ICB-4 links are both defined as CBP channel paths. Additionally, an ICB-3 link must be connected to another ICB-3 link, and an ICB-4 link must be connected to another ICB-4 link.
    • The ICP channel path must be connected to another ICP channel path. Connect an ICP channel path to another ICP channel path by specifying the CPATH keyword in the CHPID statement for every ICP channel path.
    • The CIB channel path must be connected to another CIB channel path. Connect a CIB channel path to another CIB channel path by specifying the CSYSTEM and CPATH keywords in the CHPID statement for every CIB channel path.
    • The CS5 channel path must be connected to another CS5 channel path. Connect a CS5 channel path to another CS5 channel path by specifying the CSYSTEM and CPATH keywords in the CHPID statement for every CS5 channel path.
    • The CL5 channel path must be connected to another CL5 channel path. Connect a CL5 channel path to another CL5 channel path by specifying the CPATH and optionally the CSYSTEM keywords in the CHPID statement for every CL5 channel path.
    • The CL6 channel path must be connected to another CL6 channel path. Connect a CL6 channel path to another CL6 channel path by specifying the CPATH and optionally the CSYSTEM keywords in the CHPID statement for every CL6 channel path.
  • Require a control unit definition and devices to communicate with the coupling facility end of a coupling facility channel connection. Coupling facility peer channels connecting to only ESA ends of a connection do not require a control unit nor devices. Each coupling facility sender channel requires two devices. Each coupling facility peer channel defined to a control unit (and therefore connected to a CF end of a connection) requires seven devices. When connecting two 2817 or later processors with Long Reach HCA adapters (for example, HCA2-O LR), each CIB channel path in the control unit should have 32 devices defined. When connecting Short Reach ICA adapters (for example, ICA SR), each CS5 channel path in the control unit should have 8 devices defined. When connecting Coupling Express LR adapters, each CL5 and CL6 channel path in the control unit should have a minimum of 32 devices defined but IOCP tests for a minimum of eight. When connecting 2 ICP channel paths, each ICP channel path in the control unit should have a minimum of 7 or 8 devices (see Table 2 to determine the number of ICP devices your CPC supports).

You can configure coupling facility channels as follows: