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Hierarchical scheduling algorithms for near-line tape libraries

Robotic tape libraries (RTLs) currently enjoy a prominent place in the storage market, with a reported average annual growth rate approaching 34%, primarily due to their low cost per MB figures. Given the ever-increasing requirements for storage of several modern applications, this will continue to hold. However, despite this fact and the fact that their access times continue to be very slow (e.g., tens of seconds) the central issue of efficiently scheduling accesses to RTLs has not received the attention it deserves. The paper contributes a study of efficient scheduling algorithms for tape based robotic storage libraries. It contributes novel algorithms and experimentally evaluates their performance, comparing them against that of well-known algorithms found in other environments. The paper's main contribution, hierarchical scheduling algorithms, can offer significant performance improvements, such as approximately 50% shorter average service times, while at the same time providing fair schedules.