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Formal models for safety analysis of a Data Center system

Abstract : A Data Center (DC) is a building whose purpose is to host IT devices to provide different internet services. To ensure constant operation of these devices, energy is provided by the electrical system, and to keep them at a constant temperature, a cooling system is necessary. Each of these needs must be ensured continuously, because the consequence of breakdown of one of them leads to an unavailability of the whole DC system, and this can be fatal for a company.In our Knowledge, there exists no safety and performance studies’, taking into account the whole DC system with the different interactions between its sub-systems. The existing analysis studies are partial and focus only on one sub-system, sometimes two. The main objective of this thesis is to contribute to the safety analysis of a DC system. To achieve this purpose, we study, first, each DC sub-system (electrical, thermal and network) separately, in order to define their characteristics. Each DC sub-system is a production system and consists of combinations of components that transform entrance supplies (energy for the electrical system, air flow for the thermal one, and packets for the network one) into exits, which can be internet services. Currently the existing safety analysis methods for these kinds of systems are inadequate, because the safety analysis must take into account not only the internal state of each component, but also the different production flows circulating between components. In this thesis, we consider a new modeling methodology called Production Trees (PT) which allows modeling the relationship between the components of a system with a particular attention to the flows circulating between these components.The PT modeling technique allows dealing with one kind of flow at once. Thus its application on the electrical sub-system is suitable, because there is only one kind of flows (the electric current). However, when there are dependencies between sub-systems, as in thermal and network sub-systems, different kinds of flows need to be taken into account, making the application of the PT modeling technique inadequate. Therefore, we extend this technique to deal with dependencies between the different kinds of flows in the DC. Accordingly it is easy to assess the different safety indicators of the global DC system, taking into account the interactions between its sub-systems. Moreover we make some performance statistics. We validate the results of our approach by comparing them to those obtained by a simulation tool that we have implemented based on Queuing Network theory.So far, Production Trees models are not tool supported. Therefore we propose a solution method based on the Probability Distribution of Capacity (PDC) of flows circulating in the DC system. We implement also the PT model using the AltaRica 3.0 modeling language, and use its dedicated stochastic simulator to estimate the reliability indices of the system. This is very important to compare and validate the obtained results with our assessment method. In parallel, we develop a tool which implements the PT solution algorithm with an interactive graphical interface, which allows creating, editing and analyzing PT models. The tool allows also displaying the results, and generates an AltaRica code, which can be subsequently analyzed using the stochastic simulator of AltaRica 3.0 tool.
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Mokhtar Walid Bennaceur. Formal models for safety analysis of a Data Center system. Modeling and Simulation. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLV078⟩. ⟨tel-02448316⟩

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