CTC configuration planning

When configuring CTCs for large volumes of XCF traffic some additional configuration planning needs to be done. CTC I/O will use SAP capacity, and large XCF environments can generate I/O rates much higher than traditional DASD and Tape workloads.

The SAP acts as an offload engine for the CPUs. Different processor models have different numbers of SAPs, and a spare 9672 PU can be configured as an additional SAP processor. SAP functions include:

Execution of ESA/390 I/O operations. The SAP (or SAPs) are part of the I/O subsystem of the CPC and act as Integrated Offload Processor (IOP) engines for the other processors.
Machine check handling and reset control
Support functions for Service Call Logical Processor (SCLP)

In high volume XCF environments planning should be done to ensure the CTC configuration is defined so the CTC I/O load is spread across all available SAPs. Information on channel to SAP relationships can be found in the IOCP User's Guide and ESCON® CTC Reference, GC38-0401-11. Additional Information on 9672 SAP performance and tuning can be found in WSC Flash 9646E at http://www.ibm.com/support/techdocs/.