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Reconnection Priority Algorithm on Channel Interfaces of Storage Director

IP.com Disclosure Number: IPCOM000062694D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Disbrow, JR: AUTHOR [+4]

Abstract

A Reconnection Priority algorithm implemented in a DASD (Direct Access Storage Device) subsystem for reassigning the priority of non-synchronous Storage Director-initiated channel selections is disclosed. Reconnection priority is reassigned in order to balance the channel utilization, and thus maximize system throughput especially in systems having several channels serving CPUs doing similar work with a common DASD subsystem. The purpose of a reconnection priority algorithm is to overcome biases that cause a Disk Storage Director to give preference to some of its attached channels. A first bias arises from unequal transmission delays of channel cables due to unequal channel cable lengths that give shorter cable channels a constant advantage.

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Reconnection Priority Algorithm on Channel Interfaces of Storage Director

A Reconnection Priority algorithm implemented in a DASD (Direct Access Storage Device) subsystem for reassigning the priority of non-synchronous Storage Director-initiated channel selections is disclosed. Reconnection priority is reassigned in order to balance the channel utilization, and thus maximize system throughput especially in systems having several channels serving CPUs doing similar work with a common DASD subsystem. The purpose of a reconnection priority algorithm is to overcome biases that cause a Disk Storage Director to give preference to some of its attached channels. A first bias arises from unequal transmission delays of channel cables due to unequal channel cable lengths that give shorter cable channels a constant advantage. A second bias arises from the difference in channel response time between channels of different types favoring channels having faster response times. A third bias arises from the fact that prior Storage Directors have priority schemes for choosing between simultaneous channel selections that bias in favor of the selection of certain fixed channels. The following is a description of a Rotating Reconnection Priority algorithm which is one example of a method that overcomes the biases discussed above. In the Rotating Reconnection Priority algorithm, the channel interfaces on the Storage Director are assigned sequential priorities by the Storage Director. F...