6947ch07.fm

Draft Document for Review April 7, 2004 6:15 pm

Cost benefits are realized by enabling the use of non-standalone Coupling Facilities (for example, ICFs) for all resource sharing and data sharing environments.

7.3.2 CF Structure Duplexing

System-managed Coupling Facility structure duplexing creates a duplexed copy of the structure in advance of any failure, providing a robust failure recovery capability through failover to the unaffected structure instance. This results in:

￿An easily-exploited common framework for duplexing the structure data contained in any type of CF structure, with installation control over which structures are duplexed

￿Minimized overhead of duplexing during mainline operation via hardware-assisted serialization and synchronization between the primary and secondary structure updates

￿Maximized availability in failure scenarios by providing a rapid failover to the unaffected structure instance of the duplexed pair, with very little disruption to the ongoing execution of work by the exploiter and applications

System-managed duplexing rebuild provides robust failure recovery capability via the redundancy of duplexing, and low exploitation cost via system-managed, internalized processing. Structure failures, CF failures, or losses of CF connectivity can be handled by:

1.Hiding the observed failure condition from the active connectors to the structure, so that they do not perform unnecessary recovery actions

2.Switching over to the structure instance that did not experience the failure

3.Re-establishing a new duplex copy of the structure if appropriate as the Coupling Facility becomes available again, or on a third CF in the Parallel Sysplex

System messages are generated as the structure falls back to simplex mode for monitoring and automation purposes. The structure operates in simplex mode until a new duplexed structure can be established, and can be recovered using whatever existing recovery techniques are supported by the exploiter.

System-managed duplexing's main focus is providing thisrobust recovery capability for structures whose users do not support user-managed duplexing rebuild processes, or do not even support user-managed rebuild at all.

7.3.3 Configuration planning

A new connectivity requirement for system-managed CF structure duplexing is that there must be bi-directional CF-to-CF connectivity between each pair of CFs in which duplexed structure instances reside. With peer links, this connectivity can be provided by a single bi-directional link (two with redundancy).

CF-to-CF links can either be dedicated or shared via MIF. They can be shared with z/OS-to-CF links between z/OS and Coupling Facility images in the pair of servers they connect. When planning sharing links, remember that receiver links cannot be shared, and peer links can only be shared by one Coupling Facility partition.

168IBM eServer zSeries 990 Technical Guide

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IBM 990 manual CF Structure Duplexing, Configuration planning
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990 specifications

The IBM 990 series, often referred to in the context of IBM's pioneering efforts in the realm of mainframe computing, represents a unique chapter in the history of information technology. Introduced in the late 1960s, the IBM 990 series was designed as a powerful tool for enterprise-level data processing and scientific calculations, showcasing the company's commitment to advancing computing capabilities.

One of the main features of the IBM 990 was its architecture, which was built to support a wide range of applications, from business processing to complex scientific computations. The system employed a 32-bit word length, which was advanced for its time, allowing for more flexible and efficient data handling. CPUs in the IBM 990 series supported multiple instructions per cycle, which contributed significantly to the overall efficiency and processing power of the machines.

The technology behind the IBM 990 was also notable for its use of solid-state technology. This provided a shift away from vacuum tube systems that were prevalent in earlier computing systems, enhancing the reliability and longevity of the hardware. The IBM 990 series utilized core memory, which was faster and more reliable than the magnetic drum memory systems that had been standard up to that point.

Another defining characteristic of the IBM 990 was its extensibility. Organizations could configure the machine to suit their specific needs by adding memory, storage, and peripheral devices as required. This modular approach facilitated the growth of systems alongside the technological and operational demands of the business environments they served.

In terms of software, the IBM 990 series was compatible with a variety of operating systems and programming environments, including FORTRAN and COBOL, enabling users to access a broader array of applications. This versatility was a significant advantage, making the IBM 990 an appealing choice for educational institutions, research facilities, and enterprises alike.

Moreover, the IBM 990 was engineered to support multiprocessing, which allowed multiple processes to run simultaneously, further increasing its effectiveness in tackling complex computing tasks.

In summary, the IBM 990 series represents a significant advancement in computing technology during the late 20th century. With a robust architecture, versatile configuration options, and a focus on solid-state technology, the IBM 990 facilitated substantial improvements in data processing capabilities, making it a cornerstone for many businesses and academic institutions of its time. Its impact can still be seen today in the continued evolution of mainframe computing.
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