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Technique for Unexpected Data Attention Handling

IP.com Disclosure Number: IPCOM000034547D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Fasig, JL: AUTHOR

Abstract

This technique improves performance of the AS400 Storage Subsystem by eliminating queueing delays resulting from unexpected data attentions. In DFCI-based storage systems, it is advantageous for the controller to transfer the command packet to the DFCI slave before setting up the data transfer because this permits the time spent initializing the controller hardware to be overlapped with the DASD seek time, which is typically several milliseconds. However, occasionally the disk is already at the desired disk cylinder position and the slave raises its Attention signal for data transfer before the DASD I/O processor has finished its setup.

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Technique for Unexpected Data Attention Handling

This technique improves performance of the AS400 Storage Subsystem by eliminating queueing delays resulting from unexpected data attentions. In DFCI-based storage systems, it is advantageous for the controller to transfer the command packet to the DFCI slave before setting up the data transfer because this permits the time spent initializing the controller hardware to be overlapped with the DASD seek time, which is typically several milliseconds. However, occasionally the disk is already at the desired disk cylinder position and the slave raises its Attention signal for data transfer before the DASD I/O processor has finished its setup. Ordinarily, this would not be a problem because the DASD I/O processor does not look for data attentions from a slave when no data transfer involving that slave is set up, but in heavily utilized storage subsystems there is sometimes a data transfer set up for a different facility under the same slave so that data attention polling is active when the slave raises attention and the facility radial response is received from the slave. If the radial response identifies a data attention from a particular slave and facility and the DASD I/O processor is not expecting a data attention from that slave/facility (because of incomplete setup), then that response is called an "unexpected data attention". AS400 Storage Subsystem HWC handles this condition by suspending data attention polling at the respective slave and keeping track of which slaves had data attention polling suspended because of an unexpected data attention from that slave. When data transfer initialization is complete, polling is re...