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Bus Modelling in Zoned Disks RAID Storage Systems

Peter G. Harrison, Soraya Zertal

Electronic Journal Article
PASM 2008. Proceedings of the Third International Workshop on the Practical Application of Stochastic Modelling, Palma-de-Mallorca, September 2008
March, 2009
Electronic Notes in Theoretical Computer Science
Volume 232
DOI 10.1016/j.entcs.2009.02.047

A model of bus contention in a Multi-RAID storage architecture is presented. Based on an M/G/1 queue, the main issues are to determine the service time distribution that accurately represents the highly mixed input traffic of requests. This arises from the coexistence of different RAID organisations that generate several types of physical request (read/write for each RAID level) with different related sizes. The size distributions themselves are made more complex by the striping mechanism, with full/large/small stripes in RAID5. We show the impact of the bus traffic on the system's overall performance as predicted by the model and validated against a simulation of the hardware, using common workload assumptions.

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