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1 LRI - Laboratoire de Recherche en Informatique 2 GRAND-LARGE - Global parallel and distributed computing LRI - Laboratoire de Recherche en Informatique, LIFL - Laboratoire d-Informatique Fondamentale de Lille, UP11 - Université Paris-Sud - Paris 11, Inria Saclay - Ile de France, CNRS - Centre National de la Recherche Scientifique : UMR8623 3 GRAAL - Algorithms and Scheduling for Distributed Heterogeneous Platforms Inria Grenoble - Rhône-Alpes, LIP - Laboratoire de l-Informatique du Parallélisme 4 LIP - Laboratoire de l-Informatique du Parallélisme 5 IUF - Institut Universitaire de France 6 UIUC - Department of Computer Science UIUC

Abstract : This paper introduces two new tape archival policies that can im- prove tape archive performance in certain regimes, compared to the classical RAIT Redundant Array of Independent Tapes policy. The first policy, PARALLEL, still requires as many parallel tape drives as RAIT but pre-computes large data stripes that are written contiguously on tapes to increase write-read performance. The second policy, VERTICAL, writes contiguous data into a single tape, while updating error correcting information on the fly and delaying its archival until enough data has been archived. This second approach reduces the number of tape drives used for every user request to one. The performance of the three RAIT, PARALLEL and VERTICAL policies is assessed through extensive simulations, using a hardware configuration and a distribution of I-O requests similar to these expected on the Blue Waters system. These simulations show that VERTICAL is the most suitable policy for small files, whereas PARALLEL must be used for files larger than 1 GB. We also demonstrate that RAIT never outperforms both proposed policies, and that a heterogeneous policies mixing VERTICAL and PARALLEL performs 10 times better than any other policy.

Author: Franck Cappello - Mathias Jacquelin - Loris Marchal - Yves Robert - Marc Snir -



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