Comparing archival policies for Blue Waters

Franck Cappello 1, 2 Mathias Jacquelin 3, 4 Loris Marchal 3, 4 Yves Robert 3, 4, 5 Marc Snir 6
2 GRAND-LARGE - Global parallel and distributed computing
CNRS - Centre National de la Recherche Scientifique : UMR8623, Inria Saclay - Ile de France, UP11 - Université Paris-Sud - Paris 11, LIFL - Laboratoire d'Informatique Fondamentale de Lille, LRI - Laboratoire de Recherche en Informatique
3 GRAAL - Algorithms and Scheduling for Distributed Heterogeneous Platforms
Inria Grenoble - Rhône-Alpes, LIP - Laboratoire de l'Informatique du Parallélisme
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a single tape, while updating error correcting information on the fly and delaying its archival until enough data has been archived.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.
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Franck Cappello, Mathias Jacquelin, Loris Marchal, Yves Robert, Marc Snir. Comparing archival policies for Blue Waters. [Research Report] RR-7583, INRIA. 2011. ⟨inria-00580599v2⟩

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