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The LHC Computing Grid: why distributed computing?

The primary reason for the decision to adopt a distributed computing approach to managing LHC data was money. In 1999, when work began on the design of the computing system for LHC data analysis, it rapidly became clear that the required computing capacity was far beyond the funding capacity available at CERN. On the other hand, most of the laboratories and universities collaborating on the LHC had access to national or regional computing facilities. The obvious question was: Could these facilities be somehow integrated to provide a single LHC computing service? The rapid evolution of wide area networking—increasing capacity and bandwidth coupled with falling costs—made it look possible. From there, the path to the LHC Computing Grid was set.

Additional benefits of a distributed system

During the development of the LHC Computing Grid, many additional benefits of a distributed system became apparent:

• Multiple copies of data can be kept in different sites, ensuring access for all scientists involved, independent of geographical location.
• Allows optimum use of spare capacity for multiple computer centres, making it more efficient.
• Having computer centres in multiple time zones eases round-the-clock monitoring and the availability of expert support.
• No single points of failure.
• The cost of maintenance and upgrades is distributed, since individual institutes fund local computing resources and retain responsibility for these, while still contributing to the global goal.
• Independently managed resources have encouraged novel approaches to computing and analysis.
• So-called “brain drain”, where researchers are forced to leave their country to access resources, is reduced when resources are available from their desktop.
• The system can be easily reconfigured to face new challenges, making it able to dynamically evolve throughout the life of the LHC, growing in capacity to meet the rising demands as more data is collected each year.
• Provides considerable flexibility in deciding how and where to provide future computing resources.
• Allows community to take advantage of new technologies that may appear and that offer improved usability, cost effectiveness or energy efficiency.

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