Bus Modelling in Zoned Disks RAID Storage Systems

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.