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Concept

Disponibilité

vignette|500px|La disponibilité est le rapport entre la durée de fonctionnement et la durée disponible pour le fonctionnement. Dans le domaine de l'ingénierie de fiabilité, la disponibilité d'un équipement ou d'un système est une mesure de performance. Cet indicateur-qualité est obtenu en divisant la durée durant laquelle ledit équipement ou système est opérationnel par la durée totale durant laquelle on aurait souhaité qu'il le soit. On exprime classiquement ce ratio sous forme de pourcentage. Définition Par définition, la disponibilité est l'aptitude d'un bien/d'une entité à être en état d'accomplir une fonction requise dans des conditions données, à un instant donné ou pendant un intervalle de temps donné, en supposant que la fourniture des moyens extérieurs nécessaires soit assuréeNorme française X 60-500 : terminologie relative à la fiabilité-maintenabilité-disponibilité, AFNOR, octobre 1988.. Il ne faut pas confondre la disponibilité avec la « rapidité d

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Publications associées (22)

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Cours associés (15)

This course consists of two parts:

architecture of automation systems, hands-on lab
handling of faults and failures in real-time systems, including fault-tolerant computing

This course provides a deep understanding of the concepts behind data management systems. It covers fundamental data management topics such as system architecture, data models, query processing and optimization, database design, storage organization, and transaction management.

This hands-on course teaches the tools & methods used by data scientists, from researching solutions to scaling up prototypes to Spark clusters. It exposes the students to the entire data science pipeline, from data acquisition to extracting valuable insights applied to real-world problems.

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Ingénierie de fiabilité

L'ingénierie de fiabilité est un domaine de l'ingénierie, qui traite de l'étude, de l'évaluation et du Product Lifecycle Management de la fiabilité : l'habilité d'un système ou d'un composant à rempli

Ingénierie des systèmes

L'ingénierie des systèmes ou ingénierie système est une approche scientifique interdisciplinaire, dont le but est de formaliser et d'appréhender la conception et la validation de systèmes complexes.

Tolérance aux pannes

vignette|Fichier GIF animé de 8 algorithmes ECT dans un réseau 802.1aq. La source est surlignée en violet, la destination en jaune. Les lignes violettes sont des chemins entre la source et la destinat

Experimental Validation of the Suitability of Virtualization-Based Replication for Fault Tolerance in Real-Time Control of Electric Grids

Jean-Yves Le Boudec, Jalal Mostafa, Wajeb Saab, Seyed Alireza Sanaee Kohroudi

Real-time control systems (RTCSs) perform complex control and require low response times. They typically use third-party software libraries and are deployed on generic hardware, which suffer from delay faults that can cause serious damage. To improve availability and latency, the controllers in RTCSs are replicated on physical nodes. As physical replication is expensive, we study the alternative of exploiting virtualization technology to run multiple virtual replicas on the same physical node. As virtual replicas share the same resources, the delay faults they experience might be correlated, which would make such a replication method unsuitable. We conduct several experiments with an RTCS for electric grids, with multiple virtual replicas of its controller. We find that although the delay of a virtual machine is higher than of a physical machine, the correlation between high delays among the virtual replicas is insignificant, causing an overall improved availability.We conclude that virtual replication is indeed applicable to certain RTCSs, as it can improve reliability without added cost.

2018

Chargement

Improving availability with recursive microreboots: a soft-state system case study

George Candea

Even after decades of software engineering research, complex computer systems still fail. This paper makes the case for increasing research emphasis on dependability and, specifically, on improving availability by reducing time-to-recover. All software fails at some point, so systems must be able to recover from failures. Recovery itself can fail too, so systems must know how to intelligently retry their recovery. We present here a recursive approach, in which a minimal subset of components is recovered first; if that does not work, progressively larger subsets are recovered. Our domain of interest is Internet services; these systems experience primarily transient or intermittent failures that can typically be resolved by rebooting. Conceding that failure-free software continues eluding us for years to come, we undertake a systematic investigation of fine grain component-level restarts, microreboots, as high availability medicine. Building and maintaining an accurate model of large Internet systems is nearly impossible, due to their scale and constantly evolving nature, so we take an application-generic approach, that relies on empirical observations to manage recovery. We apply recursive microreboots to Mercury, a commercial off-the-shelf (COTS)-based satellite ground station that is based on an Internet service platform. Mercury has been in successful operation for over 3 years. From our experience with Mercury, we draw design guidelines and lessons for the application of recursive microreboots to other software systems. We also present a set of guidelines for building systems amenable to recursive reboots, known as "crash-only software systems"

2004

Chargement

Reducing recovery time in a small recursively restartable system

George Candea, Pranav Garg

We present ideas on how to structure software systems for high availability by considering MTTR/MTTF characteristics of components in addition to the traditional criteria, such as functionality or state sharing. Recursive restartability (RR), a recently proposed technique for achieving high availability, exploits partial restarts at various levels within complex software infrastructures to recover from transient failures and rejuvenate software components. Here we refine the original proposal and apply the RR philosophy to Mercury, a COTS-based satellite ground station that has been in operation for over 2 years. We develop three techniques for transforming component group boundaries such that time-to-recover is reduced, hence increasing system availability. We also further RR by defining the notions of an oracle, restart group and restart policy, while showing how to reason about system properties in terms of restart groups. From our experience with applying RR to Mercury, we draw design guidelines and lessons for the systematic application of recursive restartability to other software systems amenable to RR

2002

Chargement

This course consists of two parts:

architecture of automation systems, hands-on lab
handling of faults and failures in real-time systems, including fault-tolerant computing

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