Internal Coupling Facility (Icf) - IBM Z9 Planning Manual

Internal Coupling Facility (ICF)

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You can purchase and install one or more ICF features for use in coupling facility
LPs. With this feature, the coupling facility runs on special ICF CPs that no
customer software can utilize. This allows the coupling facility function to be
performed on the CPC without affecting the model group and thus without impacting
software licensing costs for the CP resources utilized by the coupling facility. See
"Considerations for Coupling Facilities using Internal Coupling Facility (ICF) CPs" on
page 3-31.
These features are ordered separately, and are distinguished at the hardware level
from any Integrated Features for Linux (IFLs), Integrated Facility for Applications
(IFAs) features, and zIIPs. ICFs, IFLs, IFAs, or zIIPs are perceived by the system
as multiple resource pools.
With the CFCC Enhanced Patch Apply process, you can perform a disruptive install
of new CFCC code on an ICF image by simply deactivating and then reactivating
the CF image, without the much greater disruption of a Power On Reset (POR) of
the entire CEC that contains the CF image. This greatly improves the availability
characteristics of using ICFs.
ICFs are ideal for coupling resource sharing sysplexes (sysplexes that are not in
production data sharing with IMS, DB2 or VSAM/RLS). You can simplify systems
management by using XCF structures instead of ESCON CTC connections.
IBM does not recommend use of ICFs for most coupling facility structures involved
in data sharing because of the possibility of "double outages" involving the
simultaneous loss of an ICF image and one or more z/OS system images that are
using the ICF for data sharing. Depending on the structure, a double outage can
result in a significantly more involved recovery than a single outage of either an ICF
image or a z/OS image in isolation from one another.
With the use of System-Managed CF Structure Duplexing for all relevant data
sharing structures, it is possible to have a production data-sharing configuration that
uses only 2 or more internal CFs, because duplexing avoids the "single point of
failure" failure-isolation issue.
ICFs on stand-alone coupling facilities need configuration planning to account for
storage and channels. ICFs will likely increase storage requirements for the CPC
with an ICF installed, especially if software exploits the coupling facility to provide
additional function not available except when running a coupling facility in a parallel
sysplex.
The following table indicates the maximum number of ICFs that you can install on a
given model.
CPC Model
System z9 BC
Model R07
Model S07
System z9 EC
Model S08
Model S18
Model S28
Model S38
Model S54
Maximum Number of ICF's Supported
6
7
8
16
16
16
16
Chapter 2. Planning Considerations
2-41