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The storage hierarchy is a natural structure, given the set of available technologies and their price and performance characteristics. The physical structure of the storage subsystem is described, and the flow of data through the system is traced. The concept of a storage hierarchy is discussed, and the specific components of the IBM storage hierarchy from the processor high-speed buffer (HSB) to the on-line DASD configuration are described in detail. Trade-offs between technologies and the interactions among the levels of the hierarchy are discussed. In particular, the importance of the I/O boundary, processor storage volatility, and data sharing are highlighted. A continuous increase in virtual storage capacity can be seen in the evolution of large-scale operating systems, and MVS/ESA™ now provides the ultimate virtual capacity and function. New virtual structures available in MVS/ESA are discussed, and their relationship to the storage hierarchy is studied. The importance of storage to the performance and cost of a large processing system leads to a discussion of guidelines for storage configuration and data placement within the hierarchy.
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