The z/OS sysplex

A sysplex refers to a tightly-coupled cluster of independent instances of the z/OS operating system.

It is beyond of the scope of this information to go into details on how the sysplex functions. Instead, this section will help you understand the aspects of a sysplex as it applies to TCP/IP.

A sysplex can be either basic or parallel. A basic sysplex can communicate using channel to channel (CTC) connections between LPARs. Parallel Sysplex uses something called a Coupling Facility (CF).

Note: The Parallel Sysplex Coupling Facility can run either as a separate LPAR or within a dedicated hardware device. It is capable of managing data structures on behalf of applications requiring inter-LPAR communication.

Logically speaking, a sysplex is a group of distinct instances of the z/OS operating system. A distinct instance is often called an image. The z/OS images could be running in separate CPCs, or they could be running in separate LPARs within a single CPC, or it could be combination of both: a few LPARs in one CPC and a few LPARs in another CPC.

What makes a group of such z/OS images into a sysplex is the inter-image communication. This inter-image communication is normally handled through the cross-system Coupling Facility, or XCF.

XCF communications function in either a basic sysplex or in a Parallel Sysplex. If a Coupling Facility exists, a choice can be made as to whether XCF uses CTCs or the Coupling Facility to communicate.