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Over the years, data centers have been evolving to meet the new demands of cloud computing platforms, e-commerce, social networking services, and big data. These large data centers must meet various dependability requirements to guarantee the quality of service at a high level of reliability and availability, reducing interoperability time, as this is a major competitive factor for companies. The cooling system plays an important role in the availability of data centers. It is responsible for keeping the IT system at a suitable temperature to avoid hardware and software failures since operating at high temperatures negatively impacts the reliability of the electronic components. This paper investigates reliability and availability metrics and performs parametric sensitivity analysis for data center cooling systems. Our approach is based on modeling reliability block diagrams and the sensitivity analysis technique; the last is to assess how sensitive the availability is about model component failure and repair times. [ABSTRACT FROM AUTHOR]

The design-building of IT services in data centers has been historically conducted by applying rigorous IT service design-building phases-workflows. Consequently, relevant research has been conducted upon these rigorous phases-workflows to provide theoretical foundations and practical guidance to IT service design-building architects. However, the current dynamic business-governmental environment is demanding agile approaches, and research from this perspective is still very scarce. This research, thus, aims to provide an updated review and quantitative evaluation of the main rigorous (ITIL v2011, CMMI-SVC v1.3, and ISO/IEC 20000-1:2018) and main agile (ITIL v4, VeriSM, and ISO/IEC 29110-4-3) IT service design-building phases-workflows. For this aim, we conduct a conceptual review research methodology enhanced with an analytics hierarchical process (AHP) method to assess quantitatively how well these six IT service design-building phases-workflows fit two theoretical expected rigorous and agile IT service design-building phases-workflows pro formas. We found that the ITIL v2011 and CMMI-SVC v1.3 phases-workflows fit the rigorous pro forma with a high level, and the ISO/IEC 20000-1:2018 fits a moderate level, whereas all these three ones fit a low level the agile pro forma, as it was expected. ITIL v4 and VeriSM were found to fit a high level the agile pro forma but the ISO/IEC 29110-4-3 fits a moderate level. Unexpectedly, ITIL v4 and the ISO/IEC 29110-4-3 fit a moderate and moderate levels the rigorous pro forma, but VeriSM fits a low level as it was expected. Hence, we can conclude that ITIL v4 and VeriSM provide the most agile IT service design-building phase-workflow, and CMMI-SVC v1.3 the most rigorous one. The ISO/IEC 20000-1:2018 and ISO/IEC 29110-4-3 standards are still aligned to the rigorous approach, and ITIL v4 exhibits a dual moderate rigorous and high agile profile. Hence, this research provides ITSM professionals with an updated analysis useful to guide the selection and application of the IT service design-building phase-workflow—rigorous or agile one—in data centers. This research also contributes to the IT service design-building literature with updated insights and proposes specific research avenues to advance our scientific knowledge on how to design-building IT services. [ABSTRACT FROM AUTHOR]

The systematic design, building and implementation of IT services for on-premise, cloud-based or hybrid data centers are a hard engineering and managerial process. Heavyweight IT service design workflows—from ITIL v2011, CMMI-SVC v1.3 and the ISO/IEC 20000 standard—have been used in the last decade. However, the current dynamic business requirements demand to accelerate IT service design, building and implementation. Consequently, agile workflows—from ITIL v4 and VeriSM—or lightweight ones—from ISO/IEC 29110-4-3 standard and FitSM—have been proposed. However, despite these IT service design workflows provide high valuable content, they are still reported in a coarse-grain level, and thus academics and practitioners interested in using to them must add ad-hoc roles, activities-tasks, and artifacts-templates. In this research, we address this relevant knowledge gap, and using a Design Science Research Methodology (DSRM), we elaborate and evaluate exploratory an agile IT service design workflow—called AVS_FD_MVITS—that provides fine-grain content regarding roles, activities-tasks and artifacts-templates. AVS_FD_MVITS was designed using design components taken from Scrum-XP and ITIL v4 IT service design workflows. To evaluate exploratory AVS_FD_MVITS, we applied it in a realistic case in an academic small data center. The exploratory qualitative-based evaluation suggests that AVS_FD_MVITS can be considered a valid agile IT service design workflow useful for academics and practitioners. However, confirmatory quantitative-based evaluations are asked for advancing this research stream. [ABSTRACT FROM AUTHOR]

VMP (Virtual Machine Placement) is a crucial technology for energy consumption optimization of the cloud data center. Existing works mainly focus on virtual machine consolidation to increase resource utilization and reduce computing energy consumption. However, existing studies usually ignore the thermal effect that an intensive workload on IT (Information Technology) equipment can raise energy consumption by cooling systems and generate hotspots. In addition, an excessive number of virtual machine migrations increases migration costs and risks violating the SLA (Service Level Agreement) signed with users. In this paper, we present a comprehensive system model and formulate the problem as a constrained multi-objective optimization. We propose a novel thermal-aware VMP strategy to solve the problem by jointly considering virtual machines' migration cost, energy consumption, and heat recirculation around server racks. Our strategy makes placement decisions using MOPFGA (Multi-objective algorithm based on Pathfinder Algorithm and Genetic Algorithm) that combines classic MOPFA and GA enhanced by OBL (Opposition Based Learning) for fast convergence and avoidance of local optimum. Extensive experiments based on CloudSim using real data center workload data from PlanetLab show that our algorithm overcomes the defects of the MOPFA (multi-objective pathfinder algorithm) and GA (genetic algorithm) and significantly improves the overall efficiency of a data center. Compared with several state-of-the-art algorithms, MOPFGA on average reduces virtual machine migrations by 77.52%, increases CRAC (Computer Room Air Conditioner) supply temperature by 1.24%, and reduces cooling energy consumption by 24.78% and computational energy consumption by 23.62%. [ABSTRACT FROM AUTHOR]

With the development of information technology, there is a need for computational works everywhere and every time. Thus, people should be able to carry out their heavy computations without having the burden of purchasing expensive hardware and software. Cloud computing is an attractive solution to such needs, but the high energy consumption of physical machines in a Cloud data center is a matter of great concern. Therefore, some of the low-loaded machines can be turned off or switched into low energy mode using server consolidation approaches. In this paper, a Stochastic Process-Based Dynamic Server Consolidation (SB-DSC) policy is developed to reduce the total cost of data centers while satisfying the required quality of service. A novel algorithm, which we call it Stochastic Process-Based BFD (SBBFD), is employed in SB-DSC policy to perform virtual machine placements over time. SBBFD overcomes most drawbacks of other algorithms proposed in the literature. The simulation results on real workload data show that SB-DSC leads to a noticeable reduction in total cost in terms of power consumption, SLA violations, number of mode switching and number of migrations. [ABSTRACT FROM AUTHOR]

Data center network (DCN) is the core of cloud computing and accounts for 40% energy spend when compared to cooling system, power distribution and conversion of the whole data center (DC) facility. It is essential to reduce the energy consumption of DCN to ensure energy-efficient (green) data center can be achieved. An analysis of DC performance and efficiency emphasizing the effect of bandwidth provisioning and throughput on energy proportionality of two most common switch-centric DCN topologies: three-tier (3T) and fat tree (FT) based on the amount of actual energy that is turned into computing power are presented. Energy consumption of switch-centric DCNs by realistic simulations is analyzed using GreenCloud simulator. Power-related metrics were derived and adapted for the information technology equipment processes within the DCN. These metrics are acknowledged as subset of the major metrics of power usage effectiveness and data center infrastructure efficiency, known to DCs. This study suggests that although in overall FT consumes more energy, it spends less energy for transmission of a single bit of information, outperforming 3T. [ABSTRACT FROM AUTHOR]

Cloud storage is widely used by both individual and organizational users due to the many benefits, such as scalability, ubiquitous access, and low maintenance cost (and generally free for individual users). However, there are known security and privacy issues in migrating data to the cloud. To ensure or verify data integrity, a number of cloud data integrity checking schemes with different properties have been presented in the literature. Most existing schemes were subsequently found to be insecure or have high computation and communication costs. More recently in 2016, Yu et al. (Future Gener Comput Syst 62:85-91, 2016) proposed an identity-based auditing scheme for checking the integrity of cloud data. However, in this paper, we reveal that the scheme is vulnerable to data recovery attack. We also present a new identity-based public auditing scheme and formally prove the security of the scheme under the RSA assumption with large public exponents in the random oracle model. We then evaluate the performance of our proposed scheme and demonstrate that in comparison with Yu et al.'s scheme, our proposal is more practical in real-world applications. [ABSTRACT FROM AUTHOR]

This work analyzes a new and very subtle kind of security threat that can affect large-scale cloud-based IT service infrastructures, by exploiting the computational resources of their component data center to waste as much energy as possible. The consequence of these threats ranges from increased costs in the energy bill, to penalization for exceeding the agreed quantity of greenhouse gases (GHG) emissions, up to complete denial of service caused by electrical outages due to power budget exhaustion. We analyzed different types of such attacks with their potential impacts on the energy consumption, modeled their behavior and quantified how current energy-proportional technologies may provide attackers with great opportunities for raising the target facility emissions and costs. These efforts resulted in a simple model with some parametric reference values that can be used to estimate the impact of such attacks also in presence of very large infrastructures containing thousands or millions of servers. [ABSTRACT FROM AUTHOR]

The twenty-first century has witnessed major technological changes that have transformed the way we live, work, and interact with one another. One of the major technology enablers responsible for this remarkable transformation in our global society is the deployment and use of Information and Communication Technology (ICT) equipment. In fact, today ICT has become highly integrated in our society that includes the dependence on ICT of various sectors, such as business, transportation, education, and the economy to the point that we now almost completely depend on it. Over the last few years, the energy consumption resulting from the usage of ICT equipment and its impact on the environment have fueled a lot of interests among researchers, designers, manufacturers, policy makers, and educators. We present some of the motivations driving the need for energy-efficient communications. We describe and discuss some of the recent techniques and solutions that have been proposed to minimize energy consumption by communication devices, protocols, networks, end-user systems, and data centers. In addition, we highlight a few emerging trends and we also identify some challenges that need to be addressed to enable novel, scalable, cost-effective energy-efficient communications in the future. [ABSTRACT FROM AUTHOR]