IBM Parallel Sysplex

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.

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);

Parallel Sysplex

Schematic representation of a Parallel Sysplex

The forerunner to Parallel Sysplex was Virtual Coupling, a technique which allowed up to 12 IBM ESA/390 systems to execute jobs in parallel. The true Parallel Sysplex was introduced with then-new mainframe models in April 1994. 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. Server Time Protocol (STP) replaced the Sysplex Timers beginning in 2005 for System z mainframe models z990 and newer. 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.

The IBM Systems Journal dedicated a full issue to all the technology components.

Geographically Dispersed Parallel Sysplex

Geographically Dispersed Parallel Sysplex (GDPS) is an extension of Parallel Sysplex of mainframes located, potentially, in different cities. GDPS includes configurations for single site or multiple site configurations:

• GDPS/HyperSwap Manager: It is a synchronous Peer to Peer Remote Copy (PPRC) technology for use within a single data center. Data is copied from the primary storage device to a secondary storage device. In the event of a failure on the primary storage device, the system automatically makes the secondary storage device the primary, usually without disrupting running applications.
• GDPS/PPRC: It is a synchronous data mirroring technology (PPRC) that can be used on mainframes 200 kilometres (120 mi) apart. In a two-system model, both sites can be administered as if they were one system. In the event of a failure of a system or storage device, recovery can occur with limited or no data loss automatically.
• GDPS/XRC: It is an asynchronous Extended Remote Copy (XRC) technology with no restrictions on distance. XRC copies data on storage devices between two sites such that only a few seconds of data may be lost in the event of a failure. If a failure does occur, a user must initiate the recovery process. Once initiated, the process is automatic in recovering from secondary storage devices and reconfiguring systems.
• GDPS/GM: It is an asynchronous IBM Global Mirror technology with no restrictions on distance. It is designed to recovery from a total failure at one site. It will activate secondary storage devices and backup systems.
• GDPS/MGM & GDPS/MzGM: These are configurations for systems with more than two systems/sites for purposes of disaster recovery. GDPS/MGM and GDPS/MzGM are based on GDPS/PPRC and GDPS/XRC, respectively.

See also

• System z
• LPAR

External links

• IBM Parallel Sysplex site
• IBM GDPS page