Evaluation Techniques for Storage Hierarchies

efJicient storage hierorchies generally involves the repeated running of " typical " program address traces through a simulated storage system while various hierarchy design parameters are djusted. This paper describes a new and eficient method of determining, in one pass of an address trace, performance measures for a large class of demand-paged, multilevel storage systems utilizing a variety of mapping schemes and replacement algorithms. The technique depends on an algorithm classification, called " stack algorithms, " examples of which are " least frequently used, " " least recently used, " " optimal, " and " random replacement " algorithms. The techniques yield the exact access frequent-v to each storage device, which can be used to estimate the overall performance of actual storage hierarchies. Increasing speed and size demands on computer systems have resulted in corresponding demands on storage systems. Since it has been generally recognized that the speed and capacity requirements of storage systems cannot be fulfilled at an acceptable cost-performance level within any single technology, storage hierarchies that use a variety of technologies have been investigated. Several previous papers describe the general concepts of hierarchy d e ~ i g n " ~ and e v a l ~ a t i o n , ~-~ whereas others deal with specific hierarchy systems, such as the core-drum combination on the ICT Atlas c o m p ~ t e r " ~ and the cache-core combination on the IBM System/360, Model 85.'0'11 This paper introduces an efficient technique called " stack processing " that can be used in the cost-performance evaluation of a large class of storage hierarchies. The technique depends on a classification of page replacement algorithms as " stack algorithms " for which various properties are derived. These properties may be of use in the general areas of program modeling and system analysis, as well as in the evaluation of storage hierarchies. For a better understanding of storage hierarchies, we briefly review some basic concepts of their design.