Availability measurement of grid services from the perspective of a scientific computing centre

The Karlsruhe Institute of Technology (KIT) is the merger of Forschungszentrum Karlsruhe and the Technical University Karlsruhe. The Steinbuch Centre for Computing (SCC) was one of the first new organizational units of KIT, combining the former Institute for Scientific Computing of Forschungszentrum Karlsruhe and the Computing Centre of the University. IT service management according to the worldwide de-facto-standard 'IT Infrastructure Library (ITIL)' was chosen by SCC as a strategic element to support the merging of the two existing computing centres located at a distance of about 10 km. The availability and reliability of IT services directly influence the customer satisfaction as well as the reputation of the service provider, and unscheduled loss of availability due to hardware or software failures may even result in severe consequences like data loss. Fault tolerant and error correcting design features are reducing the risk of IT component failures and help to improve the delivered availability. The ITIL process controlling the respective design is called Availability Management. This paper discusses Availability Management regarding grid services delivered to WLCG and provides a few elementary guidelines for availability measurements and calculations of services consisting of arbitrary numbers of components.