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In computing, a '''Parallel Sysplex''' is a [[computer cluster|cluster]] of [[IBM mainframe]]s 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 computing|high performance]] and [[high availability]].
==Sysplex==
In 1990, [[IBM]] [[mainframe computer]]s introduced the concept of a '''Systems Complex''', commonly called a '''Sysplex''', with [[MVS]]/ESA SPV4.1. This allows authorized components in up to eight logical partitions ("[[LPAR]]s") to communicate and cooperate with each other using the [[XCF protocol]].
Components of a Sysplex include:
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==Parallel Sysplex==
[[File:GDPS.svg|thumb|300px|Schematic representation of a Parallel Sysplex]]
The Parallel Sysplex was introduced with the addition of the [[Coupling Facility]] (CF) with coupling links for high speed communication, with MVS/ESA V5.1 operating system support, together with the mainframe models in April 1994.<ref>{{cite web |url=http://www.redbooks.ibm.com/redbooks/pdfs/sg244356.pdf |title=Archived copy |
The Coupling Facility (CF) may reside on a dedicated stand-alone server configured with processors that can run Coupling Facility control code (CFCC), as integral processors on the mainframes themselves configured as ICFs (Internal Coupling Facilities), or less common, as normal LPARs. The CF contains Lock, List, and Cache structures to help with serialization, message passing, and buffer consistency between multiple LPARs.<ref>http://www.ibm.com/common/ssi/fcgi-bin/ssialias?infotype=SA&subtype=WH&attachment=ZSW01971USEN.PDF&appname=STGE_ZS_ZS_USEN&htmlfid=ZSW01971USEN Coupling Facility Configuration Options .</ref>
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* Dynamic Session Balancing
* Dynamic Transaction Routing
* Scalable capacity
Databases running on the System z server that can take advantage of this include:
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* Adabas
* DataCom
* Oracle
Other components can use the Coupling Facility to help with system management, performance, or reduced hardware requirements. Called “Resource Sharing”, uses include:
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Multi-system enclave management for improved performance
* XCF Star – Reduced hardware requirements and simplified management of XCF communication paths
Major components of a Parallel Sysplex include:
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==Server Time Protocol==
Maintaining accurate time is important in computer systems. For example, in a transaction-processing system the recovery process reconstructs the transaction data from log files. If time stamps are used for transaction-data logging, and the time stamps of two related transactions are transposed from the actual sequence, then the reconstruction of the transaction database may not match the state before the recovery process.
Server Time Protocol (STP) can be used to provide a single time source between multiple servers. Based on Network Time Protocol concepts, one of the System z servers is designated by the HMC as the primary time source (Stratum 1). It then sends timing signals to the Stratum 2 servers through use of coupling links. The Stratum 2 servers in turn send timing signals to the Stratum 3 servers. To provide availability, one of the servers can be designated as a backup time source, and a third server can be designated as an “Arbiter” to assist the Backup Time Server in determining if it should take the role of the Primary during exception conditions.
STP has been available on System z servers since 2005.
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