Evolving ATLAS computing for today's networks.
The ATLAS computing infrastructure was designed many years ago based
on the assumption of rather limited network connectivity between computing centers.
ATLAS sites have been organized in a hierarchical model, where only a static subset
of all possible network links can be exploited and a static subset of well connected
sites (CERN and the T1s) can cover important functional roles such as
hosting master copies of the data.
The pragmatic adoption of such simplified approach, in respect of a more relaxed
scenario interconnecting all sites, was very beneficial during the commissioning of the
ATLAS distributed computing system and essential in reducing the
operational cost during the first two years of LHC data taking.
In the mean time, networks evolved far beyond this initial scenario: while a few countries are still
poorly connected with the rest of the WLCG infrastructure, most of the ATLAS computing
centers are now efficiently interlinked. Our operational experience in running the
computing infrastructure in the last years demonstrated many limitations of the current model:
statically defined network paths are sometimes abused, while most of the network links are underutilized together
with computing and storage resources at many sites, under the wrong assumption
of limited connectivity with the rest of the infrastructure.
In this contribution we describe the various steps which ATLAS Distributed Computing
went through in order to benefit from the network evolution and move from the current
static model to a more relaxed scenario. This will include the development of monitoring
and testing tools and the commissioning effort. We will finally describe the
gains of the new model in terms of resource utilization at grid sites after many months of experience.
- Track: Distributed Processing and Analysis on Grids and Clouds
- Author: Simone Campana
- Co-authors: Fernando Harald Barreiro Megino, Cedric Serfon, Ikuo Ueda, Stephane Jezequel
- Presentation Type: parallel
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SimoneCampana - 11-Oct-2011