Abstract
The XRootD software framework is essential for data access at WLCG sites. The WLCG community is exploring and expanding XRootD functionality. This presents a particular challenge at the RAL Tier-1 as the Echo storage service is a Ceph based Erasure Coded object store. External access to Echo uses gateway machines which run GridFTP and caching servers. Local jobs access Echo via caches on every worker node, but it is clear there are inefficiencies in the system. Remote jobs also access data via XRootD on Echo. For CMS jobs this is via the AAA service. ATLAS, who are consolidating their storage at fewer sites, are increasingly accessing job input data remotely. This paper describes the continuing work to optimise both local and remote data access by testing different caching methods.
Highlights
The UK Tier 1 is situated at the Rutherford Appleton Laboratory (RAL) and supports all LHC experiments, as well as a growing number of others in HEP, Astronomy and Space Science
All 32 unique files were processed in 36 minutes when maximally parallelized compared with 278 minutes when all of the resource was used by a single job
The CMS AAA service is designed to provide partial or full datasets to any CMS User without the need to download it to local storage
Summary
The UK Tier 1 is situated at the Rutherford Appleton Laboratory (RAL) and supports all LHC experiments, as well as a growing number of others in HEP, Astronomy and Space Science. Access to Echo is primarily via XRootD [3], which is both a protocol name and an open source suite of fast and highly scalable data access tools commonly used by LHC experiments. XRootD is designed to use with file systems organised in directories. Echo is not a file system in the traditional sense and does not use a directory structure. Instead it contains objects, which can be named so as to keep the appearance of a directory structure, e.g. The entire path is a string which defines the object name
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