Simulation Studies of the Cassette Migration Activities in a Scalable Tape Archiver

摘要

With the proliferation of multimedia applications, even secondary storage systems do not have sufficient storage capacity to meet the demand, only tertiary storage systems can provide the necessary storage economically. We have been examining the feasibility of "scalable tape archiver" where any number of commodity 8mm based robotics can be connected to allow the development of arbitrary sized archives economically. 8mm tape based robotics which can mechanically exchange cassette tapes through a special transportation port were designed and built. By migrating the frequently accessed, HOT, cassettes evenly amongst the archivers in both the foreground and background, we can improve the performance of the system significantly compared with systems without the ability to migrate cassettes. In this paper, we analyze the migration activities on scalable tape archiver. When heat imbalance is detected, migration activities are invoked, which we examined in detail through simulations using the parameters taken from the real archivers. The case where a file is striped over several tapes is also carefully examined. In addition, in our system, even when some of the drives fail, the system can continue unaffected by dynamically migrating the cassettes to the archivers which have working drives. We examined the migration activiites when drive failure ocucrs. Our simulation study clarified the effectiveness of the scalable tape archiver.