XRootD plug-in based solutions for site specific require-ments

Jan Knedlik,Kilian Schwarz,Paul Kramp,Thorsten Kollegger,A Forti,M Litmaath,P Hristov,L Betev,O Smirnova

doi:10.1051/epjconf/201921404005

Jan Knedlik, Kilian Schwarz + Show 7 more

Open Access

https://doi.org/10.1051/epjconf/201921404005

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Abstract

XRootD† has been established as a standard for WAN data access in HEP and HENP. Site specific features, like those existing at GSI, have historically been hard to implement with native methods. XRootD allows a custom replacement of basic functionality for native XRootD functions through the use of plug-ins. XRootD clients allow this since version 4.0. In this contribution, our XRootD based developments motivated by the use in the current ALICE Tier 2 Centre at GSI and the upcoming ALICE Analysis Facility will be shown. Among other things, an XRootD redirector plug-in which redirects local clients directly to a shared file system, as well as the needed changes to the XRootD base code, which are publicly available since XRootD version 4.8.0, will be presented. Furthermore, a prototype for an XRootD based disk caching system for opportunistic resources has been developed.

Highlights

GSI has long standing experience with operating an XRootD service, the established software standard for WAN data access in HEP and HENP
ROOT1 has been established as the software standard framework for data analysis in HEP and HENP and is heavily used in local environments and jobs runnning inside the WLCG
Getting vector read limits is unnecessary for the shared filesystem, since the reads will be splitted into asynchronous filesystem calls anyway. Using these changes it is possible to use a ROOT setup in which jobs and user-code running in ROOT significantly boosts I/O performance when running inside a site where the XRootD data resides on top of a POSIX compliant filesystem which is handled by an XRootD data server

Summary

Introduction

GSI has long standing experience with operating an XRootD service, the established software standard for WAN data access in HEP and HENP. Accessing the scientific data, stored ontop of the HPC infrastructure at the ALICE Tier 2 centre and the ALICE Analysis Facility prototype at GSI, revealed multiple challenges and requirements. To allow efficient utilization of such HPC centers into the more open grid world, multiple solutions to adjust such software frameworks to the need of the infrastructure at GSI have already been deployed. This article describes the current state of development for XRootD based solutions for low latency access to the shared file system at GSI, especially XRootD client & server plug-ins. With the current storage infrastructure at GSI, namely the access to Lustre through the XRootD data servers, the following room for improvement has been identified: 1. As an improvement to the previous solution, an XRootD client plug-in, which had to be loaded by all clients running on GSI’s HPC farm, an XRootD redirector plug-in has been developed

RedirLocal: A plug-in to redirect clients to local files

Changes to XRootD

Enabling local redirection in ROOT for high performance data processing

XRootD Disk Caching Proxy for opportunistic resources

Findings

Conclusion