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Coupling Facility
In IBM System/390 and IBM Z mainframe computers, a Coupling Facility or CF is a piece of computer hardware or virtual machine that coordinates multiple processors.
A Parallel Sysplex relies on one or more Coupling Facilities (CFs). A coupling facility is a mainframe processor (runs in an own LPAR, with dedicated physical CP, defined through Hardware Management Console (HMC)), with memory and special channels (CF Links), and a specialized operating system called Coupling Facility Control Code (CFCC). It has no I/O devices, other than the CF links. The information in the CF resides entirely in memory as CFCC is not a virtual memory operating system. A CF typically has a large memory – of the order of several tens of gigabytes. The CF runs no application software.
When originally introduced, the CFCC executed in a separate 9674 mainframe unit that was essentially a processor without I/O facilities other than the CF links. Later IBM enabled the use of an Internal Coupling Facility where the CFCC runs in a logical partition (LPAR) defined in standard processor complex and communicates over internal links within that processor complex hardware. Internal links are simulated, whereas links to another processor unit are over copper or optical fiber cables. More than one CF is typically configured in a Sysplex cluster for reliability and availability. Recovery support in the z/OS operating system allows structures to be rebuilt in the alternate CF in the event of a failure.
Supported by CFs, a Sysplex cluster scales very well up to several hundreds of CPUs (in up to 32 members, each with up to 190 CPUs) running transaction and data base applications. Using the CF links, data can be directly exchanged between the CF memory and the memory of the attached systems, using a direct memory access like mechanism, without interrupting a running program. Systems in a Sysplex cluster store CF information in local memory in an area called a bit vector. This enables them to locally query critical state information of other systems in the Sysplex without the need for issuing requests to the CF. The System z Architecture includes 18 special machine instructions and additional hardware features supporting CF operation.
A CF is used for three purposes:
These three purposes are catered for by three types of structure:
A structure is a dedicated portion of CF memory. It is said to be connected to by specific CF-exploiting applications on the coupled z/OS systems. A typical Parallel Sysplex contains several structures of each type. Each software exploiter may use several structures of each type. For example, each Db2 Data Sharing Group uses one Lock structure, one List structure and several cache structures (one for each Group Buffer Pool (GBP)).
Structures may be duplexed across different CFs, allowing two copies of the same structure to be kept synchronized. Duplexing is often used as part of an installation's drive to remove single points of failure, with the aim of reducing the incidence and duration of application outages. In the event of the failure of one CF, the other copy of the structure is used to satisfy all requests.
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Coupling Facility
In IBM System/390 and IBM Z mainframe computers, a Coupling Facility or CF is a piece of computer hardware or virtual machine that coordinates multiple processors.
A Parallel Sysplex relies on one or more Coupling Facilities (CFs). A coupling facility is a mainframe processor (runs in an own LPAR, with dedicated physical CP, defined through Hardware Management Console (HMC)), with memory and special channels (CF Links), and a specialized operating system called Coupling Facility Control Code (CFCC). It has no I/O devices, other than the CF links. The information in the CF resides entirely in memory as CFCC is not a virtual memory operating system. A CF typically has a large memory – of the order of several tens of gigabytes. The CF runs no application software.
When originally introduced, the CFCC executed in a separate 9674 mainframe unit that was essentially a processor without I/O facilities other than the CF links. Later IBM enabled the use of an Internal Coupling Facility where the CFCC runs in a logical partition (LPAR) defined in standard processor complex and communicates over internal links within that processor complex hardware. Internal links are simulated, whereas links to another processor unit are over copper or optical fiber cables. More than one CF is typically configured in a Sysplex cluster for reliability and availability. Recovery support in the z/OS operating system allows structures to be rebuilt in the alternate CF in the event of a failure.
Supported by CFs, a Sysplex cluster scales very well up to several hundreds of CPUs (in up to 32 members, each with up to 190 CPUs) running transaction and data base applications. Using the CF links, data can be directly exchanged between the CF memory and the memory of the attached systems, using a direct memory access like mechanism, without interrupting a running program. Systems in a Sysplex cluster store CF information in local memory in an area called a bit vector. This enables them to locally query critical state information of other systems in the Sysplex without the need for issuing requests to the CF. The System z Architecture includes 18 special machine instructions and additional hardware features supporting CF operation.
A CF is used for three purposes:
These three purposes are catered for by three types of structure:
A structure is a dedicated portion of CF memory. It is said to be connected to by specific CF-exploiting applications on the coupled z/OS systems. A typical Parallel Sysplex contains several structures of each type. Each software exploiter may use several structures of each type. For example, each Db2 Data Sharing Group uses one Lock structure, one List structure and several cache structures (one for each Group Buffer Pool (GBP)).
Structures may be duplexed across different CFs, allowing two copies of the same structure to be kept synchronized. Duplexing is often used as part of an installation's drive to remove single points of failure, with the aim of reducing the incidence and duration of application outages. In the event of the failure of one CF, the other copy of the structure is used to satisfy all requests.