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Reliability, Availability and Serviceability Within IPL Functions of a Duplex Control System

IP.com Disclosure Number: IPCOM000052367D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Combes, J: AUTHOR [+2]

Abstract

The article describes Reliability, Availability and Serviceability (RA features within Initial Program Load (IPL) functions of a duplex control system which consists of two stored program controllers sharing two diskette units via an I/O bus. The IPL process is structured into steps regarding diskette activity, and the availability of one diskette unit is sufficient to put the system into operation. Diskette unit verification procedure, the capability of loading a diskette diagnostic program in case of diskette unit failure, and a trouble-shooting facility in case of double diskette unit or bus failures are provided.

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Reliability, Availability and Serviceability Within IPL Functions of a Duplex Control System

The article describes Reliability, Availability and Serviceability (RA features within Initial Program Load (IPL) functions of a duplex control system which consists of two stored program controllers sharing two diskette units via an I/O bus. The IPL process is structured into steps regarding diskette activity, and the availability of one diskette unit is sufficient to put the system into operation. Diskette unit verification procedure, the capability of loading a diskette diagnostic program in case of diskette unit failure, and a trouble-shooting facility in case of double diskette unit or bus failures are provided.

The purpose of IPL is to transfer the program into the main storage of one or both controllers from the shared diskette units. IPL is structured into steps to be processed in a controller while being transparent to the other controller diskette activity. Upon a diskette unit request, if the diskette unit is busy for the other controller, the request is reissued for the maximum duration of a diskette unit usage for the other controller. When a diskette unit is obtained, a limited data transfer takes place, and, as soon as this data transfer is completed, the diskette unit is released to be available to the other controller.

To reduce system vulnerability to a single IPL device failure, program distribution between the two diskettes and the IPL functions is such that the availability of one diskette unit only is sufficient to put the system into operation, even when the maintenance personnel have left.

The IPL programs needed to load any requested program are assigned to the diskette which contains the operational program, the so-called primary diskette.

Maintenance personnel can mount the primary diskette on any diskette unit and load the IPL programs into any controller to put the system into operation . from diskette unit 1 when diskette unit 2 is out of order; . from diskette unit 2 when diskette unit 1 is out of order.

If repair of a diskette unit cannot be done at once because of the lack of a spare part, the maintenance personnel may leave the system with: . the primary diskette on diskette unit 1 and diskette unit 2 out of order; . the primary diskette on diskette unit 2 and diskette unit 1 out of order.

When IPL is requested by the customer, as initial IPL operations are addressed to diskette unit 1, the IPL will work at once in the first case; in the second case an error being detected on diskette unit 1, the IPL will back up automatically to diskette unit 2 and the system will be restored anyway.

To provide mainte...