Abstract

Pressures from both WLCG VOs and externalities have led to a desire to "simplify" data access and handling for Tier-2 resources across the Grid. This has mostly been imagined in terms of reducing book-keeping for VOs, and total replicas needed across sites. One common direction of motion is to increasing the amount of remote-access to data for jobs, which is also seen as enabling the development of administratively-cheaper Tier-2 subcat-egories, reducing manpower and equipment costs. Caching technologies are often seen as a "cheap" way to ameliorate the increased latency (and decreased bandwidth) introduced by ubiquitous remote-access approaches, but the usefulness of caches is strongly dependant on the reuse of the data thus cached. We report on work done in the UK at four GridPP Tier-2 sites - ECDF, Glasgow, RALPP and Durham - to investigate the suitability of transparent caching via the recently-rebranded XCache (Xrootd Proxy Cache) for both ATLAS and CMS workloads, and to support workloads by other caching approaches (such as the ARC CE Cache).

Highlights

  • The provision of computing and storage resources across the WLCG, and especially in the UK under GridPP, is subject to increasing requirements to improve efficiency, in terms of both cost and staffing

  • In the UK, the effect of this pressure on storage resource provision has been to drive a move towards "simplifying" storage[1], in accordance with survey results suggesting that Grid storage services were responsible for a significant fraction of the FTEs needed to run a site

  • This impetus is in alignment with a general desire from the WLCG Experiments, and in particular ATLAS, to have a simpler, more streamlined view of the resource available to them

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Summary

Introduction

The provision of computing and storage resources across the WLCG, and especially in the UK under GridPP, is subject to increasing requirements to improve efficiency, in terms of both cost and staffing. In the UK, the effect of this pressure on storage resource provision has been to drive a move towards "simplifying" storage[1], in accordance with survey results suggesting that Grid storage services were responsible for a significant fraction of the FTEs needed to run a site This impetus is in alignment with a general desire from the WLCG Experiments, and in particular ATLAS, to have a simpler, more streamlined view of the resource available to them. The UK is host to a large number of Tier-2 facilities, for historical reasons, which are grouped into "Regional Tier-2" units as represented in figure 1 This grouping is loosely administrative, but all Tier-2s expose separate compute and storage resources, making GridPP the most “endpoint-rich" region in WLCG. One approach for mitigating all of these issues has been the implementation of various "caches" at storageless sites, in order to prevent excess transfer of data and to allow that data which has been transferred to potentially be accessed at lower cost

Caching Approaches
ARC Cache at UKI-SCOTGRID-DURHAM
Future Work and Recommendations

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