6947ch07.fm

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

￿Simplified I/O definition

The connection between managed channels and managed control units does not have to be explicitly defined.

￿Reduced skills required to manage z/OS

Managed channels and control units are automatically monitored, balanced, tuned, and reconfigured.

￿Enhanced availability

A failing or hung channel path will result in reduced throughput on the affected control unit. DCM will rapidly detect the symptom and augment the paths, automatically bypassing the problem. The problem will still have to be analyzed and corrected by site personnel.

DCM will automatically analyze and minimize single points of failure on an I/O path by selecting appropriate paths. DCM is sensitive to single points of failure such as:

–ESCON or FICON channel cards

–I/O CHA cards

–Processor Self-Timed Interconnect

–Director port cards

–Control Unit I/O bay

–Control Unit Interface card

–ESCON Director

7.5.3Channel Subsystem Priority Queueing

Channel Subsystem (CSS) Priority Queueing is a new function available on zSeries processors in either 1basic or LPAR mode. It allows the z/OS operating system to specify a priority value when starting an I/O request. When there is contention causing queueing in the Channel Subsystem, the request is prioritized by this value.

An extension of I/O priority queuing, a concept that has been evolving in MVS over the past few years. If important work is missing its goals due to I/O contention on channels shared with other work, it will be given a higher Channel Subsystem I/O priority than the less important work. This function goes hand in hand with the Dynamic Channel Path Management described previously: as additional channel paths are moved to control units to help an important workload meet goals, Channel Subsystem Priority Queuing ensures that the important work receives greater access to additional bandwidth than less important work that happen to be using the same channel.

Channel Subsystem Priority Queuing runs on a zSeries server in z/Architecture mode, in both basic and LPAR mode. The participating z/OS system images can be defined as XCFLOCAL, MONOPLEX, or MULTISYSTEM. It is optimized when WLM is running in goal mode. It does not require a Coupling Facility structure.

Enabling Channel Subsystem Priority Queuing involves defining a range of I/O priorities for each logical partition on the hardware management console, and then turning on the “Global input/output (I/O) priority queuing” switch. (You also need to specify “YES” for WLM's I/O priority management setting.)

z/OS will set the priority based on a goal mode WLM policy. This complements the goal mode priority management that sets I/O priority for IOS UCB queues, and for queueing in the 2105 ESS disk subsystem.

1The z990 operates in LPAR mode only

180IBM eServer zSeries 990 Technical Guide

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IBM 990 manual Channel Subsystem Priority Queueing
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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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