Defining multiple logical channel subsystems

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IOCP has been dramatically enhanced to allow the definition of an I/O configuration containing multiple, logical channel subsystems. A logical channel subsystem (CSS) is a complete definition of logical partitions, channels, control units, and devices as you might have defined for any previous CPC. The difference with this level of IOCP and the CPCs it supports is that multiple CSSs can be defined with each CSS containing logical partitions, channels, control units, and devices. In addition, some CPCs now support multiple subchannel sets, which allows a CSS to have more than twice as many devices.

IOCP has added the CSS parameter to many traditional keywords to identify the logical channel subsystem to which the keyword parameters apply. IOCP has introduced a new keyword, SCHSET, to the IODEVICE statement to identify the subchannel set in a CSS to which a device belongs. See IOCP statements and functions for complete syntax rules for using the CSS parameter and specifying the SCHSET keyword. The following list summarizes the new keywords and parameters in IOCP in support of multiple logical channel subsystems and multiple subchannel sets:

RESOURCE statement: Previously the RESOURCE statement defined the logical partitions (LPs) and associated partition numbers (now called MIF image IDs) to be included in the configuration. With this level of IOCP, you prefix those values with a CSS ID. The LPs and MIF image IDs are defined in the specified CSS.
Note: What was called "partition number" in previous levels of IOCP is now called MIF image ID. It retains all the same characteristics (for example, a hex number from 1-F), and is used the same for CTC control unit definitions. However, for CPCs that ICP IOCP supports, the MIF image ID is no longer used in the PARTITION keyword of the CF statement in the policy information defined for the site's coupling facility resource management (CFRM) policy. Instead, the "partition ID" that is specified on the activation profile for the CF image on the Support Element identifies the CF image.
CHPID statement: The PATH parameter has traditionally been used to mirror the CHPID number assigned by the CPC to the actual channel that is being defined. With ICP IOCP and the CPCs it supports, the PATH parameter specifies a logical CHPID number of your choosing. The PATH parameter allows the user to specify the CSSs and the CHPID number that is assigned to a channel path. If it is a physical channel (for example, FICON), the new PCHID keyword identifies the location of the physical channel in the CPC. For internal channels (for example internal coupling), the PCHID keyword is not allowed, and only the logical CHPID number is required.
When a channel path is defined to multiple CSSs using the PATH parameter, the channel path is defined as spanned. The PARTITION or NOTPART keywords can also use the CSS parameter to indicate which LPs can access the channel in each CSS to which the channel path is assigned.
CNTLUNIT statement: The PATH and LINK keywords can have a CSS parameter that indicates the logical CHPIDs from each CSS that have access to the control unit and the associated destination link address for each path.
IODEVICE statement: The PATH keyword can have a CSS parameter to indicate a preferred path from each CSS for the device. Likewise, the PARTITION or NOTPART keywords can have a CSS parameter to indicate a unique device candidate list for each CSS that has access to the device. The SCHSET keyword identifies the subchannel set in a CSS to which a device belongs; it can include a CSS parameter.

Note: If you are defining a single CSS configuration, the CSS parameter is optional.