Dr Greig Cowan (University of Edinburgh)
The ScotGrid distributed Tier-2 now provides more that 4MSI2K and 500TB for LHC computing, which is spread across three sites at Durham, Edinburgh and Glasgow. Tier-2 sites have a dual role to play in the computing models of the LHC VOs. Firstly, their CPU resources are used for the generation of Monte Carlo event data. Secondly, the end user analysis object data is distributed to the site Grid storage and held on disk ready for processing by physicists analysis jobs. In this paper we show how we have designed the ScotGrid storage and data management resources in order to optimise access by physicists to LHC data. Within ScotGrid, all sites use the gLite DPM storage manager middleware but use different underlying storage and network hardware. Using the WLCG grid to submit real ATLAS and LHCb analysis code to process VO data stored on the ScotGrid sites, we present a comparison of the different architectures at the sites and the use of different data access protocols (rfio, xroot, gridftp). The results will be presented from the point of view of the end user (in terms of number of events processed/second) and from the point of view of the site which typically wants to minimise load and the impact analysis activity has on other users of the system.