Efficiently sequencing tape-resident jobs
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Constructing a video server with tertiary storage: practice and experience
Multimedia Systems
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With the recent improvements in network and processor speeds, several data intensive applications have become much more feasible than ever before. The only practical solution for storing such enormous amounts of data is tertiarystorage. Automated access to tertiary storage is made possible through robotic libraries for tapes and optical disks. Due to the slow speeds of operation of the drives and library robotics, access times for such librariesare high resulting in the accumulation of I/O requests. In this paper we study the problem of scheduling these requests for efficient performance. We focus on scheduling policies that process all requests on a loaded medium before unloading it. For single drive settings an efficient algorithm that produces optimal schedules is developed. For multiple drives the problem is shown to be NP-Complete. Efficient and effective heuristics are presented for the multiple drive case. The scheduling policies developed achieve significant performance gains over more naive policies. The algorithms developed are simple to implement and are not restrictive. The study is general enough to be applicable to any storage library handling removable media, such as tapes and optical disks.