IBM Parallel Sysplex
Encyclopedia
In computing, a Parallel Sysplex is a cluster of IBM mainframe
IBM mainframe
IBM mainframes are large computer systems produced by IBM from 1952 to the present. During the 1960s and 1970s, the term mainframe computer was almost synonymous with IBM products due to their marketshare...

s acting together as a single system image with z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...

. Used for disaster recovery, Parallel Sysplex combines data sharing and parallel computing
Parallel computing
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...

 to allow a cluster of up to 32 systems to share a workload for high performance and high availability
High availability
High availability is a system design approach and associated service implementation that ensures a prearranged level of operational performance will be met during a contractual measurement period....

.

Sysplex

In IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

 mainframe computer
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...

s, 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
    Global Resource Serialization
    Global Resource Serialization is the component within the IBM z/OS operating system responsible for enabling fair access to serially reusable computing resources, such as datasets and tape drives or virtual resources, such as lists, queues, and control blocks...

     (GRS), which allows multiple systems to access the same resources concurrently, serializing where necessary to ensure exclusive access;
  • Cross System Coupling Facility (XCF
    IBM XCF
    In IBM mainframes, a Cross-system coupling facility, or XCF, is a component of z/OS that manages communications between applications in a sysplex...

    ), which allows systems to communicate peer-to-peer
    Peer-to-peer
    Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

    ;
  • Couple Data Sets (CDS);

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
    Coupling Facility
    In IBM mainframe computers, a Coupling Facility or CF is a piece of computer hardware which allows multiple processors to access the same data.A Parallel Sysplex relies on one or more Coupling Facilities...

     (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
    Operating system
    An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

     services and, usually, middleware
    Middleware
    Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...

     such as DB2
    IBM DB2
    The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...

    ).

The Coupling Facility may be either a dedicated external system (a small mainframe, such as a System z9
System z9
IBM System z9 is a line of IBM mainframe. It was announced on July 25, 2005 and the first models were available on September 16, 2005. The System z9 also marks the end of the previously used eServer zSeries naming convention, and it is the last z/Architecture 1 machine.- Background :System z9 is a...

 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
    Peer to Peer Remote Copy
    Peer to Peer Remote Copy or PPRC is a protocol to replicate a storage volume to another control unit in a remote site. Synchronous PPRC causes each write to the primary volume to be performed to the secondary as well, and the I/O is only considered complete when update to both primary and secondary...

     (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 (124.3 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
    Extended Remote Copy
    Extended Remote Copy or XRC is an IBM zSeries and System z9 mainframe computer technology for data replication. It combines supported hardware and z/OS software to provide asynchronous replication over long distances...

     (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.

External links

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