Evaluation of tertiary models was also begun and studies were done to understand the access patterns for tertiary devices. A report summarizing the current state of the art in tertiary storage systems was prepared [4]. The report gives a comprehensive discussion of magnetic tape and optical storage technologies and a classification of commercial products based on their performance characteristics. Our analysis of product data indicates that in contrast to disk technology, tertiary storage products have significant variability in terms of transfer rates as well as other performance figures. The paper also summarizes the research efforts in the areas of operating systems, databases and advanced applications to integrate tertiary storage. Different assumptions about the underlying technology result in entirely different algorithms and system design.
Research on the problem of scheduling I/O requests for tape libraries was also begun. A simulator using the csim simulation language was developed. The simulator is general enough to model all types of tertiary libraries, including optical disks and tapes. The simulator was employed in evaluating various scheduling policies. A simpler version of the scheduling problem wherein all requests for a single medium are completed before offloading it in an off-line setting was studied. For the single drive case, an optimal algorithm was developed and for the multiple case, efficient heuristics were presented and evaluated [9]. Initial evaluation of the feasibility of intelligent prefetching for 2 dimensional data based on application access patterns was also conducted. Access to the tertiary storage at SDSC has been obtained. Efforts are underway to obtain trace data for user accesses to the tertiary storage.