What is Parallel Sysplex ?

The above diagram illustrates schematic representation of Parallel Sysplex

In IBM mainframe computers, a Systems Complex, commonly called a Sysplex, allows multiple processors to be joined into a single unit, sharing the same Sysplex name and Couple Data Sets. Put another way, a Sysplex is a single logical system running on one or more physical systems. Sysplexes are often isolated within a single system, but Parallel Sysplex technology allows multiple mainframes to act as one.

Components of a Sysplex include:

• A Sysplex Timer which synchronizes all member systems' clocks;
• Global Resource Serialization (GRS), which allows multiple systems to access the same resources concurrently, serializing where necessary to ensure exclusive access;
• Cross System Coupling Facility (XCF), which allows systems to communicate peer to peer;
• Couple Data Sets (CDS);

In computing, a Parallel Sysplex is a cluster of IBM mainframes acting together as a single system image with z/OS. Used for disaster recovery, Parallel Sysplex combines data sharing and parallel computing to allow a cluster of up to 32 systems to share a workload for high performance and high availability.

Major components of a Parallel Sysplex include:

• Coupling Facility (CF or ICF) hardware, allowing multiple processors to share, cache, update, and balance data access;
• Sysplex Timers or Server Time Protocol to synchronize the clocks of all member systems
• High speed, high quality, redundant cabling;
• Software (operating system services and, usually, middleware such as DB2).

The Coupling Facility may be either a dedicated external system (a small mainframe, such as a System z9 BC, specially configured with only coupling facility processors) or integral processors on the mainframes themselves configured as ICFs (Internal Coupling Facilities). It is recommended that at least one external CF be used in a parallel sysplex. A Parallel Sysplex has at least two CFs and/or ICFs for redundancy. Every mainframe participating in a Parallel Sysplex does not need an ICF or its own external CF — mainframes merely attach, via cables, to the external CFs or ICFs.

A Sysplex Timer is a physically separate piece of hardware from the mainframe, whereas STP is an integral facility within the mainframe's microcode.

With STP and ICFs it is possible to construct a complete Parallel Sysplex installation with two connected mainframes. Moreover, a single mainframe can contain the internal equivalent of a complete physical Parallel Sysplex, useful for application testing and development purposes.