Exploring heterogeneity of unreliable machines for p2p backup

P2P architecture is a viable option for enterprise backup. In contrast to dedicated backup servers, nowadays a standard solution, making backups directly on organization's workstations should be cheaper (as existing hardware is used), more efficient (as there is no single bottleneck server) and more reliable (as the machines are geographically dispersed). We present the architecture of a p2p backup system that uses pairwise replication contracts between a data owner and a replicator. In contrast to standard p2p storage systems using directly a DHT, the contracts allow our system to optimize replicas' placement depending on a specific optimization strategy, and so to take advantage of the heterogeneity of the machines and the network. Such optimization is particularly appealing in the context of backup: replicas can be geographically dispersed, the load sent over the network can be minimized, or the optimization goal can be to minimize the backup/restore time. However, managing the contracts, keeping them consistent and adjusting them in response to dynamically changing environment is challenging. We built a scientific prototype and ran the experiments on 150 workstations in the university's computer laboratories and, separately, on 50 PlanetLab nodes. We found out that the main factor affecting the quality of the system is the availability of the machines. Yet, our main conclusion is that it is possible to build an efficient and reliable backup system on highly unreliable machines (our computers had just 13% average availability)

A HOLISTIC REDUNDANCY- AND INCENTIVE-BASED FRAMEWORK TO IMPROVE CONTENT AVAILABILITY IN PEER-TO-PEER NETWORKS

Peer-to-Peer (P2P) technology has emerged as an important alternative to the traditional client-server communication paradigm to build large-scale distributed systems. P2P enables the creation, dissemination and access to information at low cost and without the need of dedicated coordinating entities. However, existing P2P systems fail to provide high-levels of content availability, which limit their applicability and adoption. This dissertation takes a holistic approach to device mechanisms to improve content availability in large-scale P2P systems. Content availability in P2P can be impacted by hardware failures and churn. Hardware failures, in the form of disk or node failures, render information inaccessible. Churn, an inherent property of P2P, is the collective effect of the users’ uncoordinated behavior, which occurs when a large percentage of nodes join and leave frequently. Such a behavior reduces content availability significantly. Mitigating the combined effect of hardware failures and churn on content availability in P2P requires new and innovative solutions that go beyond those applied in existing distributed systems. To addresses this challenge, the thesis proposes two complementary, low cost mechanisms, whereby nodes self-organize to overcome failures and improve content availability. The first mechanism is a low complexity and highly flexible hybrid redundancy scheme, referred to as Proactive Repair (PR). The second mechanism is an incentive-based scheme that promotes cooperation and enforces fair exchange of resources among peers. These mechanisms provide the basis for the development of distributed self-organizing algorithms to automate PR and, through incentives, maximize their effectiveness in realistic P2P environments. Our proposed solution is evaluated using a combination of analytical and experimental methods. The analytical models are developed to determine the availability and repair cost properties of PR. The results indicate that PR’s repair cost outperforms other redundancy schemes. The experimental analysis was carried out using simulation and the development of a testbed. The simulation results confirm that PR improves content availability in P2P. The proposed mechanisms are implemented and tested using a DHT-based P2P application environment. The experimental results indicate that the incentive-based mechanism can promote fair exchange of resources and limits the impact of uncooperative behaviors such as “free-riding”

Interest in Solar Photovoltaic (PV) and Peer-To-Peer Energy Trading for Back-Up Electricity in Nigerian Residential Housing Estates

Solar energy presents a highly viable alternative for backup electricity provision in urban Nigeria, as the technology is now mature. Due to widespread electricity black-outs, petrol and diesel generators are widely used, causing local air and noise pollu-tion and contributing to climate change. However, the main clean alternative, solar, has little foothold in the Nigerian energy market. The thesis explores whether households value the “clean power” benefit of the widespread adoption of solar en-ergy for backup electricity in residential estates. It employs a mixed-method ap-proach using semi-structured interviews, a survey, and a discrete choice experiment with 649 respondents in Ibadan, a Nigerian city, to provide insights into preferences for clean and quiet solar PV backup electricity on a residential estate as well as en-ergy trading preferences. Applying quantitative and qualitative methods, the study finds that consumers are interested in dwelling in estates that only permit cleaner backup alternatives, including solar and inverters, compared with the status quo op-tion of staying in estates with petrol or diesel generators. The study also finds that consumers are interested in peer-to-peer energy trading, with differences in prefer-ences for selling and buying excess electricity from neighbours. The thesis also finds that autarky aspirations and financial benefits are key factors that influence partici-pation in energy trading. The findings demonstrate that whilst the electricity supply remains unreliable, there is an opportunity for solar PV to claim a much larger share of the backup electricity market. Furthermore, policymakers and clean energy pro-viders keen to increase the uptake of residential solar energy should highlight the clean and quiet benefits of solar energy for the residents themselves. This research also demonstrates an opportunity to develop and market clean, quiet estates that appeal to people concerned about the health impacts of generator use

Innovative Financing for Renewable Energy

Carbon pollution from fossil-fuel combustion is the largest contributor to climate change worldwide. Renewable energy can materially help to reduce greenhouse gas (GHG) emissions and their principal cause, worldwide dependence on carbon fuels. If our goal is to remain at or below 1990 numbers, then fossil fuels must be phased out of the global energy portfolio. While other factors such as energy inefficiencies in buildings, appliances and transportation, for example; deforestation, farm animal excretion, pipeline leakage, HFCs for refrigeration, black soot and changes in land use also contribute to increased emissions, finding new, innovative ways to empower people to seize the opportunities presented by clean, renewable electricity present an invaluable path to reduce carbon emissions