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Limited Replacement and Migration Controls

IP.com Disclosure Number: IPCOM000046938D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Kamionka, HE: AUTHOR [+2]

Abstract

Data storage hierarchies, such as a cache to main memory, main memory to peripheral equipment, high-speed peripheral equipment to low-speed peripheral equipment, and the like, involve the migration of data from a faster data storage unit to a slower data storage unit. Such migration can be caused by the well-known LRU (least recently used) replacement algorithms or can be part of a space management of a large number of peripheral data storage units. In either event, the migration of data from an upper or faster level of a data storage hierarchy to a slower or lower level requires applications of resourcing. In a given migration time period, it may be desired to limit the migration for enhancing overall performance.

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Limited Replacement and Migration Controls

Data storage hierarchies, such as a cache to main memory, main memory to peripheral equipment, high-speed peripheral equipment to low-speed peripheral equipment, and the like, involve the migration of data from a faster data storage unit to a slower data storage unit. Such migration can be caused by the well- known LRU (least recently used) replacement algorithms or can be part of a space management of a large number of peripheral data storage units. In either event, the migration of data from an upper or faster level of a data storage hierarchy to a slower or lower level requires applications of resourcing. In a given migration time period, it may be desired to limit the migration for enhancing overall performance. In accordance with this article, an "age floor" is assigned to all migrations such that any data resident in an upper level of a data storage hierarchy is not migrated or replaced to a lower level unless it has an age exceeding the age floor. The practical effect is to limit the migration and replacement activity to a given lower level unit for spreading the migration activities over a large number of units. The age floor can be adjusted from time to time to accommodate varying environmental operating conditions. Generally, there is no easy way for a user of a data processing environment at the time of initial allocation of the data set to cause the selection of a data set volume to agree with the planned and actual usage rate of the data set. Also, the user generally does not want the job of selecting a data storage volume (DASD unit or tape volume). Various automatic volume selection techniques are employed which can selec...