Cost Analysis of Serpentine Tape Data Placement Techniques in Support of Continuous Media Display

Due to the information explosion we are witnessing, a growing number of applications store, maintain, and retrieve large volumes of continuous media (CM) data, where the data is required to be available online or near-online. These data repositories are implemented using hierarchical storage structures (HSS). One of the components of HSS is tertiary storage, which provides a cost-effective storage for the vast amount of data manipulated by these applications. However, it is crucial that the 3-4 orders of magnitude difference in access time between the tertiary storage and the secondary storage be bridged to allow online or near-online access to the tertiary resident data. This wide accessgap is mainly due to: the sequential nature of the most popular tertiary technologies (i.e., tapes) and the low number of drives per media in tertiary storage juke boxes. In this paper, we investigate the performance and cost effectiveness of three data placement techniques for serpentine tapes, in the context of CM servers, namely: 1) contiguous placement with track sharing (CP w/ sharing), 2) contiguous placement without track sharing (CP w/o sharing), and 3) Wrap ARound data Placement (WARP). We focus on tape technology because it provide the most cost effective storage for very large databases, and more specifically on serpentine tapes because they are increasingly the technology of choice for mid-range and high-end systems. We have implemented these techniques on an IBM 3590 tape drive, and compared their performances and cost effectiveness, where we use initial latency (TLatency) as the performance metric and cost per MB (CostMB) as the cost effectiveness metric. c © Springer-Verlag. Published in the Proceedings of the 10 International Conference on Computing and Information (ICCI 2000), November 18-21, 2000, Kuwait.