Oct 10 – 14, 2016
San Francisco Marriott Marquis
America/Los_Angeles timezone

Accessing Data Federations with CVMFS

Oct 13, 2016, 11:45 AM
GG C3 (San Francisco Mariott Marquis)


San Francisco Mariott Marquis

Oral Track 4: Data Handling Track 4: Data Handling


Brian Paul Bockelman (University of Nebraska (US))


Data federations have become an increasingly common tool for large collaborations such as CMS and Atlas to efficiently distribute large data files. Unfortunately, these typically come with weak namespace semantics and a non-POSIX API. On the other hand, CVMFS has provided a POSIX-compliant read-only interface for use cases with a small working set size (such as software distribution). The metadata required for the CVMFS POSIX interface distributed through a caching hierarchy, allowing it to scale to the level of about a hundred thousand hosts. In this paper, we will describe our contributions to CVMFS that merges the data scalability of XRootD-based data federations (such as AAA) with metadata scalability and POSIX interface of CVMFS. We modified CVMFS so it can serve unmodified files without copying them to the repository server. CVMFS 2.2.0 is also able to redirect requests for data files to servers outside of the CVMFS content distribution network. Finally, we added the ability to manage authorization and authentication using security credentials such as X509 proxy certificates. We combined these modifications with the OSG’s StashCache regional XRootD caching infrastructure to create a cached data distribution network. We will show performance metrics accessing the data federation through CVMFS compared to direct data federation access. Additionally, we will discuss the improved user experience of providing access to a data federation through a POSIX filesystem.

Tertiary Keyword (Optional) Storage systems
Secondary Keyword (Optional) Computing middleware
Primary Keyword (Mandatory) Distributed data handling

Primary author

Derek John Weitzel (University of Nebraska (US))


Brian Paul Bockelman (University of Nebraska (US)) Dave Dykstra (Fermi National Accelerator Lab. (US)) Jakob Blomer (CERN) Rene Meusel (CERN)

Presentation materials