Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.
Following the first full year of Large Hadron Collider (LHC) data taking, the Worldwide LHC Computing Grid (WLCG) computing environment built to support LHC data processing and analysis has been validated. In this review, I discuss the rationale for the design of a distributed system and describe how this environment was constructed and deployed through the use of grid computing technologies. I discuss the experience with large-scale testing and operation with real accelerator data, which shows that expectations have been met and sometimes exceeded. The computing system's key achievements are that (a) the WLCG infrastructure is distributed and makes use of all the dispersed resources, (b) the experiments' computing models are also distributed and can make excellent use of the infrastructure, and (c) the computing system has enabled physics output in a very short time. Finally, I present prospects for the future evolution of the WLCG infrastructure.
The computing strategy document for HL-LHC identifies storage as one of the main WLCG challenges in one decade from now. In the naive assumption of applying today's computing model, the ATLAS and CMS experiments will need one order of magnitude more storage resources than what could be realistically provided by the funding agencies at the same cost of today. The evolution of the computing facilities and the way storage will be organized and consolidated will play a key role in how this possible shortage of resources will be addressed. In this contribution we will describe the architecture of a WLCG data lake, intended as a storage service geographically distributed across large data centers connected by fast network with low latency. Will present the experience with our first prototype, showing how the concept, implemented at different scales, can serve different needs, from regional and national consolidation of storage to an international data provisioning service. We will highlight how the system leverages its distributed nature, the economy of scale and different classes of storage to optimise the hardware and operational cost, through a set of policy driven decisions concerning data placement and data retention. We will discuss how the system leverages or interoperates with existing federated storage solutions. We will finally describe the possible data processing models in this environment and present our first benchmarks.
The GridPP Collaboration is building a UK computing Grid for particle physics, as part of the international effort towards computing for the Large Hadron Collider. The project, funded by the UK Particle Physics and Astronomy Research Council (PPARC), began in September 2001 and completed its first phase 3 years later. GridPP is a collaboration of approximately 100 researchers in 19 UK university particle physics groups, the Council for the Central Laboratory of the Research Councils and CERN, reflecting the strategic importance of the project. In collaboration with other European and US efforts, the first phase of the project demonstrated the feasibility of developing, deploying and operating a Grid-based computing system to meet the UK needs of the Large Hadron Collider experiments. This note describes the work undertaken to achieve this goal. S Supplementary documentation is available from stacks.iop.org/JPhysG/32/N1. References to sections S1, S2.1, etc are to sections within this online supplement.
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