Optimization of energy efficiency in data and WEB hosting centers

Mención Internacional en el título de doctorThis thesis tackles the optimization of energy efficiency in data centers in terms of network and server utilization. For what concerns networking utilization the work focuses on Energy Efficient Ethernet (EEE) - IEEE 802.3az standard - which is the energy-aware alternative to legacy Ethernet, and an important component of current and future green data centers. More specifically the first contribution of this thesis consists in deriving and analytical model of gigabit EEE links with coalescing using M/G/1 queues with sleep and wake-up periods. Packet coalescing has been proposed to save energy by extending the sojourn in the Low Power Idle state of EEE. The model presented in this thesis approximates with a good accuracy both the energy saving and the average packet delay by using a few significant traffic descriptors. While coalescing improves by far the energy efficiency of EEE, it is still far from achieving energy consumption proportional to traffic. Moreover, coalescing can introduce high delays. To this extend, by using sensitivity analysis the thesis evaluates the impact of coalescing timers and buffer sizes, and sheds light on the delay incurred by adopting coalescing schemes. Accordingly, the design and study of a first family of dynamic algorithms, namely measurement-based coalescing control (MBCC), is proposed. MBCC schemes tune the coalescing parameters on-the-fly, according to the instantaneous load and the coalescing delay experienced by the packets. The thesis also discusses a second family of dynamic algorithms, namely NT-policy coalescing control (NTCC), that adjusts the coalescing parameters based on the sole occurrence of timeouts and buffer fill-ups. Furthermore, the performance of static as well as dynamic coalescing schemes is investigated using real traffic traces. The results reported in this work show that, by relying on run-time delay measurements, simple and practical MBCC adaptive coalescing schemes outperform traditional static and dynamic coalescing while the adoption of NTCC coalescing schemes has practically no advantages with respect to static coalescing when delay guarantees have to be provided. Notably, MBCC schemes double the energy saving benefit of legacy EEE coalescing and allow to control the coalescing delay. For what concerns server utilization, the thesis presents an exhaustive empirical characterization of the power requirements of multiple components of data center servers. The characterization is the second key contribution of this thesis, and is achieved by devising different experiments to stress server components, taking into account the multiple available CPU frequencies and the presence of multicore servers. The described experiments, allow to measure energy consumption of server components and identify their optimal operational points. The study proves that the curve defining the minimal CPU power utilization, as a function of the load expressed in Active Cycles Per Second, is neither concave nor purely convex. Instead, it definitively shows a superlinear dependence on the load. The results illustrate how to improve the efficiency of network cards and disks. Finally, the accuracy of the model derived from the server components consumption characterization is validated by comparing the real energy consumed by two Hadoop applications - PageRank and WordCount - with the estimation from the model, obtaining errors below 4:1%, on average.This work has been partially supported by IMDEA Networks Institute and the Greek State Scholarships FoundationPrograma Oficial de Doctorado en Ingeniería TelemáticaPresidente: Marco Giuseppe Ajmone Marsan.- Secretario: Jose Luis Ayala Rodrigo.- Vocal: Gianluca Antonio Rizz

Performance-aware energy optimizations in networks for HPC

Energy efficiency is an important challenge in the field of High Performance Computing (HPC). High energy requirements not only limit the potential to realize next-generation machines but are also an increasing part of the total cost of ownership of an HPC system. While at large HPC systems are becoming increasingly energy proportional in an effort to reduce energy costs, interconnect links stand out for their inefficiency. Commodity interconnect links remain ¿always-on¿, consuming full power even when no data is being transmitted. Although various techniques have been proposed towards energy- proportional interconnects, they are often too conservative or are not focused toward HPC. Aggressive techniques for interconnect energy savings are often not applied to HPC, in particular, because they may incur excessive performance overheads. Any energy-saving technique will only be adopted in HPC if there is no significant impact on performance, which is still the primary design objective. This thesis explores interconnect energy proportionality from a performance perspective. In this thesis, first a characterization of HPC applications is presented, making a case for the enormous potential for interconnect energy proportionality with HPC applications. Next, an HPC interconnect with on/off based links, modeled after the IEEE Energy Efficient Ethernet protocol, is evaluated. This evaluation while presenting a relationship between performance impact and energy over HPC applications also emphasizes the need for performance focused designs in energy efficient interconnects. Next, an adaptive mechanism, PerfBound, is presented that saves link energy subject to a bound on application performance overheads. Finally this evaluation structure is applied into an intermediate link power state, in addition to the traditional on and off states. Results of this study, over 15 production HPC applications show that, compared to current day always-on HPC interconnects, link energy can be reduced by unto 70%, while application performance overhead is bounded to only 1%.La eficiencia energética es un gran reto en el área de la Supercomputación (HPC), las grandes necesidades de energía no solo limitan el potencial de las computadoras de nueva generación, sino que también aumentan el coste de funcionamiento de estos sistemas. Mientras que los sistemas HPC tienden a ser cada vez más energéticamente proporcionales en un empeño por reducir costes, los enlaces de interconexión siguen siendo muy ineficientes. Los enlaces de interconexión comunes funcionan en modo "always-on", es decir, consumiendo energía incluso cuando no transmiten. Aunque se han propuesto algunas técnicas que ayuden a la proporcionalidad energética de los enlaces de interconexión, éstas han sido muy agresivas o poco enfocadas hacia su uso con sistemas HPC. Las técnicas de ahorro energético para los enlaces más agresivas no suelen ser utilizadas en HPC, particularmente porque degradan excesivamente el rendimiento. Cualquier técnica de ahorro energético solo será adoptada en sistemas HPC si no hay un impacto excesivo en el rendimiento, el cual es el principal objetivo de estos sistemas. En esta tesis, primeramente se presenta una nueva caracterización de aplicaciones HPC, remarcando el enorme potencial de la proporcionalidad en los enlaces de interconexión proporcionales para aplicaciones HPC. Seguidamente, se evaluará siguiendo el protocolo "IEEE Energy Efficient Ethernet" un link de interconexión on/off. Esta evaluación presentará una relación de impacto energético y rendimiento en aplicaciones HPC, enfatizando en la necesidad de usar un enlace de interconexión enfocados a la eficiencia. Se continuará con la presentación de un mecanismo adaptivo, PerfBound, que ahorra energía respetando unos límites máximos de impacto en el rendimiento. Finalmente, esta estructura es aplicada a un nuevo estado intermedio de funcionamiento adicional a los estados tradicionales on/off. Los resultados de este estudio, muestran que en más de 15 aplicaciones HPC la energía en los enlaces puede ser reducida en un 70% en comparación con enlaces "always-on", mientras que el impacto en el rendimiento es de tan solo un 1%.Postprint (published version

On energy consumption of switch-centric data center networks

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 esnure 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 (ITE) processes within the DCN. These metrics are acknowledged as subset of the major metrics of power usage effectiveness (PUE) and data center infrastructure efficiency (DCIE), known to DCs. This study suggests that despite in overall FT consumes more energy, it spends less energy for transmission of a single bit of information, outperforming 3T

Convergencia de tecnologías ópticas y Ethernet en LAN, MAN y SAN: nuevas arquitecturas, análisis de prestaciones y eficiencia energética

Mención Internacional en el título de doctorThe development of Information Technologies in the last decades, especially the last two, together with the introduction of computing devices to the mainstream consumer market, has had the logical consequence of the generalisation of the Internet access. The explosive development of the smartphone market has brought ubiquity to that generalisation, to the point that social interaction, content sharing and content production happens all the time. Social networks have all but increased that trend, maximising the diffusion of multimedia content: images, audio and video, which require high network capacities to be enjoyed quickly. This need for endless bandwidth and speed in information sharing brings challenges that affect mainly optical Metropolitan Area Networks (MANs) and Wide Area Networks (WANs). Furthermore, the wide spreading of Ethernet technologies has also brought the possibility to achieve economies of scale by either extending the reach of Ethernet Local Area Networks (LANs) to the MAN and WAN environment or even integrating them with Storage Area Networks (SANs). Finally, this generalisation of telecommunication technologies in every day life has as a consequence an important rise in energy consumption as well. Because of this, providing energy efficient strategies in networking is key to ensure the scalability of the whole Internet. In this thesis, the main technologies in all the fields mentioned above are reviewed, its core challenges identified and several contributions beyond the state of the art are suggested to improve today’s MANs andWANs. In the first contribution of this thesism, the integration between Metro Ethernet and Wavelength Division Multiplexion (WDM) optical transparent rings is explored by proposing an adaptation architecture to provide efficient broadcast and multicast. The second contribution explores the fusion between transparent WDM and OCDMA architectures to simplify medium access in a ring. Regarding SANs, the third contribution explores the challenges in SANs through the problems of Fibre Channel over Ethernet due to buffer design issues. In this contribution, analysis, design and validation with FCoE traces and simulation is provided to calculate buffer overflow probabilities in the absence of flow control mechanisms taking into account the bursty nature of SAN traffic. Finally, the fourth and last contribution addresses the problems of energy efficiency in Plastic Optical Fibres (POF), a new kind of optical fibre more suitable for transmission in vehicles and for home networking. This contribution suggests two packet coalescing strategies to further improve the energy effiency mechanisms in POFs.El desarrollo de las Tecnologías de la Información en las últimas décadas, especialmente las últimas dos, junto con la introducción de dispositivos informáticos al mercado de masas, ha tenido como consecuencia lógica la generalización del acceso a Internet. El explosivo desarrollo del mercado de teléfonos inteligentes ha añadido un factor de ubicuidad a tal generalización, al extremo de que la interacción social, la compartición y producción de contenidos sucede a cada instante. Las redes sociales no han hecho sino incrementar tal tendencia, maximizando la difusión de contenido multimedia: imágenes, audio y vídeo, los cuales requieren gran capacidad en las redes para poder obtenerse con rapidez. Esta necesidad de ancho de banda ilimitado y velocidad en la compartición de información trae consigo retos que afectan principalmente a las Redes de Área Metropolitana (Metropolitan Area Networks, MANs) y Redes de Área Extensa (Wide Area Networks, WANs). Además, la gran difusión de las tecnologías Ethernet ha traído la posibilidad de alcanzar economías de escala bien extendiendo el alcance de Ethernet más allá de las Redes de Área Local (Local Area Networks, LANs) al entorno de las MAN y las WAN o incluso integrándolas con Redes de Almacenamiento (Storage Area Networks, SANs). Finalmente, esta generalización de las tecnologías de la comunicación en la vida cotidiana tiene también como consecuencia un importante aumento en el consumo de energía. Por tanto, desarrollar estrategias de transmisión en red eficientes energéticamente es clave para asegurar la escalabilidad de Internet. En esta tesis, las principales tecnologías de todos los campos mencionados arriba serán estudiadas, sus más importantes retos identificados y se sugieren varias contribuciones más allá del actual estado del arte para mejorar las actuales MANs y WANs. En la primera contribución de esta tesis, se explora la integración entre Metro Ethernet y anillos ópticos transparentes por Multiplexión en Longitud de Onda (Wavelength Division Multiplex, WDM) mediante la proposición de una arquitectura de adaptación para permitir la difusión y multidifusión eficiente. La segunda contribución explora la fusión entre las arquitecturas transparentes WDM y arquitecturas por Accesso Dividido Múltiple por Códigos Ópticos (OCDMA) para simplificar el acceso en una red en anillo. En lo referente a las SANs, la tercera contribución explora los retos en SANs a través de los problemas de Fibre Channel sobre Ethernet debido a los problemas en el diseño de búferes. En esta contribución, se provee un análisis, diseño y validación con trazas FCoE para calcular las probabilidades de desbordamiento de buffer en ausencia de mecanismos de control de flujo teniendo en cuenta la naturaleza rafagosa del tráfico de SAN. Finalmente, la cuarta y última contribución aborda los problemas de eficiencia energética en Fibras Ópticas Plásticas (POF), una nueva variedad de fibra óptica más adecuada para la transmisión en vehículos y para entornos de red caseros. Esta contribución sugiere dos estrategias de agrupamiento de paquetes para mejorar los mecanismos de eficiencia energética en POFs.Programa Oficial de Posgrado en Ingeniería TelemáticaPresidente: Luca Valcarenghi.- Secretario: Ignacio Soto Campos.- Vocal: Bas Huiszoo

ENERGY EFFICIENT WIRED NETWORKING

This research proposes a new dynamic energy management framework for a backbone Internet Protocol over Dense Wavelength Division Multiplexing (IP over DWDM) network. Maintaining the logical IP-layer topology is a key constraint of our architecture whilst saving energy by infrastructure sleeping and virtual router migration. The traffic demand in a Tier 2/3 network typically has a regular diurnal pattern based on people‟s activities, which is high in working hours and much lighter during hours associated with sleep. When the traffic demand is light, virtual router instances can be consolidated to a smaller set of physical platforms and the unneeded physical platforms can be put to sleep to save energy. As the traffic demand increases the sleeping physical platforms can be re-awoken in order to host virtual router instances and so maintain quality of service. Since the IP-layer topology remains unchanged throughout virtual router migration in our framework, there is no network disruption or discontinuities when the physical platforms enter or leave hibernation. However, this migration places extra demands on the optical layer as additional connections are needed to preserve the logical IP-layer topology whilst forwarding traffic to the new virtual router location. Consequently, dynamic optical connection management is needed for the new framework. Two important issues are considered in the framework, i.e. when to trigger the virtual router migration and where to move virtual router instances to? For the first issue, a reactive mechanism is used to trigger the virtual router migration by monitoring the network state. Then, a new evolutionary-based algorithm called VRM_MOEA is proposed for solving the destination physical platform selection problem, which chooses the appropriate location of virtual router instances as traffic demand varies. A novel hybrid simulation platform is developed to measure the performance of new framework, which is able to capture the functionality of the optical layer, the IP layer data-path and the IP/optical control plane. Simulation results show that the performance of network energy saving depends on many factors, such as network topology, quiet and busy thresholds, and traffic load; however, savings of around 30% are possible with typical medium-sized network topologies

ENERGY AWARE TRAFFIC ENGINEERING IN WIRED COMMUNICATION NETWORKS

The reduction of power consumption in communication networks has become a key issue for both the Internet Service Providers (ISP) and the research community. Ac- cording to different studies, the power consumption of Information and Communication Technologies (ICT) varies from 2% to 10% of the worldwide power consumption [1,2]. Moreover, the expected trends for the future predict a notably increase of the ICT power consumption, doubling its value by 2020 [2] and growing to around 30% of the worldwide electricity demand by 2030 according to business-as-usual evaluation scenarios [15]. It is therefore not surprising that researchers, manufacturers and network providers are spending significant efforts to reduce the power consumption of ICT systems from dif- ferent angles. To this extent, networking devices waste a considerable amount of power. In partic- ular, their power consumption has always been increased in the last years, coupled with the increase of the offered performance [16]. Actually, power consumption of network- ing devices scales with the installed capacity, rather than the current load [17]. Thus, for an ISP the network power consumption is practically constant, unrespectively to traffic fluctuations. However, actual traffic is subject to strong day/night oscillations [3]. Thus, many devices are underutilized, especially during off-peak hours when traffic is low. This represents a clear opportunity for saving energy, since many resources (i.e., routers and links) are powered on without being fully utilized. In this context, resource consolidation is a known paradigm for the reduction of the power consumption. It consists in having a carefully selected subset of network devices entering a low power state, and use the rest to transport the required amount of traffic. This is possible without disrupting the Quality of Service (QoS) offered by the network infrastructure, since communication networks are designed over the peak foreseen traffic request, and with redundancy and over-provisioning in mind. In this thesis work, we present different techniques to perform resource consolida- tion in backbone IP-based networks, ranging from centralized solutions, where a central entity computes a global solution based on an omniscient vision of the network, to dis- tributed solutions, where single nodes take independent decisions on the local power- state, based solely on local knowledge. Moreover, different technological assumptions are made, to account for different possible directions of the network devices evolutions, ranging from the possibility to switch off linecard ports, to whole network nodes, and taking into account different power consumption profiles