To enable the communication between a Coupling Facility (CF) Logical Partition and the z/OS LPARs, special types of high-speed CF links are required. These links are important because of the impact of link performance on CF request response times. For configurations covering large distances, time spent on the link can be the largest part of CF response time.

A CF link adapter can be shared between LPs, meaning the same adapter can transfer data from/to different z/OS systems to one CF, thus reducing the number of links needed. This is called Multiple Image Facility (MIF), the same name used for FICON and ESON channels.

CF links in the System z servers work in a mode called peer mode. In this mode we have even more flexibility with connections. For example, a single link adapter can be connected (multiple image facility) to both z/OS and a CF.

Notes:

CF – Coupling Facility

ESCON – Enterprise Systems Connection

FICON – Fibre Connection

LP – Logical Partition

LPAR – Logical Partition

MIF – Multiple Image Facility

The Coupling Facility LP is defined through HCD and Processor Resource/Systems Manager (PR/SM) panels on the Hardware Management Console (HMC). Once you have defined an LP to be a coupling facility LP, only the CFCC can run in that LP. When you activate the Coupling Facility LP, the system automatically loads the CFCC from the laptop Support Element (SE) hard disk of the CPC.

Its major functions are:

• Storage management
• Support for CF links
• Console services (HMC)
• Trace, logout, and recovery functions
• Provide support for the list, cache, and lock structures

Notes:

CF – Coupling Facility

CFCC – Coupling Facility Control Code

CPC – Central Processor Complex

HCD – Hardware Configuration Definition

HMC – Hardware Management Console

LP – Logical Partition

PR/SM – Processor Resource/System Manager

Coupling Facility Control Code is an IBM licensed Internal Code that always runs under an LPAR, regardless of whether the CF is in a standalone CPC or in a general purpose CPC (where CFCC LPs are together with z/OS LPs). A standalone CPC is a CPC only allowing LPs running CFCCs.

CFCC is a simple but efficient operating system where, for example, no virtual storage support is implemented. It has multiprocessing capabilities running multiple processors and when there is no work to do, it loops in the CF link waiting for work requests (the interrupt mechanism is not implemented).

Notes:

CF – Coupling Facility

CPC – Central Processor Complex

ICF – Internal Coupling Facility

LIC – Licensed Internal Code

LP – Logical Partition

LPAR – Logical Partition

ICFs are PUs in a CPC configured to run only CFCC code. The PUs are not shipped with a fixed function assignment, but are assigned during power-on reset (POR) or later non-disruptively by on demand offerings such as: CBU, CUoD, CIU, ON/OFF CoD.

Those offerings allow the customer to convert, in seconds, a non-characterizable PU in any PU personality type such as: CPU, ICF, IFL, zAAP, zIIP and SAP.

An ICF can reduce the cost of exploiting coupling facility technology because:

• ICFs are less expensive than CPs.
• An ICF has a special software license charge. Special PR/SM microcode prevents the defined ICF PUs from executing non-CFCC code such as z/OS.

Notes:

CBU – Capacity BackUp

CFCC – Coupling Facility Control Code

CIU – Customer Initiated Upgrade

CoD – Capacity on Demand

CP – Central Processor

CPC – Central Processor Complex

CPU – Central Processor Unit

CUoD – Capacity Upgrade on Demand

ICF – Internal Coupling Facility

IFL – Integrated Facility for Linux

POR – Power-On Reset

PR/SM – Processor Resource/System Manager

PU – Processor Units

SAP – System Assistance Processor

zAAP – z Application Assist Processor

zIIP – z Integrated Information Processor

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.

With z/OS services, a component called XES allows authorized applications, such as subsystems and z/OS components, to use the coupling facility to cache data, exchange status, and access sysplex lock structures in order to implement high performance data sharing and rapid recovery from failures.

The coupling facility is defined using HCD and PR/SM panels. Once you have defined an LP to be a coupling facility, only the coupling facility control code can run in that LP. When you activate the coupling facility LP, the system automatically loads the CFCC from the support element (an internal laptop) of the CPC.

Implementing a coupling facility in your sysplex requires both hardware and software:

• CPC that supports the CFCC.
• CPCs on which one or more z/OS images run and which are capable of connecting to the coupling facility with CF links.
• Appropriate level of z/OS that allows an exploiter to access a desired function when managing the coupling facility resources.
• CFCC must implement the functions the exploiter needs.

Notes:

CF – Coupling Facility

CFCC – Coupling Facility Control Code

CPC – Central Processor Complex

HCD – Hardware Configuration Definition

LP – Logical Partition

PR/SM – Processor Resource/System Manager

XES – Cross-system Extended Services

External Time Reference hardware facility (ETR) is the generic name for IBM Sysplex Timer.

The ETR architecture provides the means of synchronizing TOD clocks in different CPCs with a centralized time reference, which in turn can be set accurately on the basis of UTC time standard (External Time Source). The architecture defines a time-signal protocol and a distribution network (called the ETR network) that permits accurate setting, maintenance, and consistency of TOD clocks.

Notes:

CPC – Central Processor Complex

TOD – Time of Day

UTC – Coordinated Universal Time

The cross-system coupling facility (XCF) component of z/OS manages communications between applications in a sysplex. XCF services allow authorized programs in a sysplex to communicate with programs on the same MVS system or other MVS systems. If a system fails, XCF services also provide the capability for batch jobs and started tasks to be restarted on another eligible system in the sysplex.

z/OS XCF allows up to 32 z/OS systems to communicate in a sysplex.