Toward sustainable data centers: a comprehensive energy management strategy

Data centers are major contributors to the emission of carbon dioxide to the atmosphere, and this contribution is expected to increase in the following years. This has encouraged the development of techniques to reduce the energy consumption and the environmental footprint of data centers. Whereas some of these techniques have succeeded to reduce the energy consumption of the hardware equipment of data centers (including IT, cooling, and power supply systems), we claim that sustainable data centers will be only possible if the problem is faced by means of a holistic approach that includes not only the aforementioned techniques but also intelligent and unifying solutions that enable a synergistic and energy-aware management of data centers. In this paper, we propose a comprehensive strategy to reduce the carbon footprint of data centers that uses the energy as a driver of their management procedures. In addition, we present a holistic management architecture for sustainable data centers that implements the aforementioned strategy, and we propose design guidelines to accomplish each step of the proposed strategy, referring to related achievements and enumerating the main challenges that must be still solved.Peer ReviewedPostprint (author's final draft

Dependability analysis of web services

Web Services form the basis of the web based eCommerce eScience applications so it is vital that robust services are developed. Traditional validation and verification techniques are centred around the concept of removing all faults to guarantee correct operation whereas Dependability gives an assessment of how dependably a system can deliver the required functionality by assessing attributes, and by eliminating threats via means attempts to improve dependability. Fault injection is a well-proven dependability assessment method. Although much work has been done in the area of fault injection and distributed systems in general, there appears to have been little research carried out on applying this to middleware systems and Web Services in particular. There are additional problems associated with applying existing fault injection technologies to Web Services running in a virtual machine environment since most are either invasive or work at a machine level. The Fault Injection Technology (FIT) method has been devised to address these problems for middleware systems. The Web Service-Fault Injection Technology (WS-FIT) implementation applies the FIT method, based on network level fault injection, to Web Services to create a non-invasive dependability assessment method. It allows targeted perturbation of Web Service RFC parameters as well as more traditional network level fault injection operations. The WS-FIT tool includes taxonomies that define a system under test, fault models to apply and failure modes to be detected, and uses these taxonomies to generate fault injection campaigns. WS-FIT has been applied to a number of case studies and has successfully demonstrated its effectiveness. It has also been successfully applied to a third-party system to evaluate dependability means. It performed this dependability assessment as well as allowing debugging of the means to be undertaken uncovering unknown faults

LCOGT Network Observatory Operations

We describe the operational capabilities of the Las Cumbres Observatory Global Telescope Network. We summarize our hardware and software for maintaining and monitoring network health. We focus on methodologies to utilize the automated system to monitor availability of sites, instruments and telescopes, to monitor performance, permit automatic recovery, and provide automatic error reporting. The same jTCS control system is used on telescopes of apertures 0.4m, 0.8m, 1m and 2m, and for multiple instruments on each. We describe our network operational model, including workloads, and illustrate our current tools, and operational performance indicators, including telemetry and metrics reporting from on-site reductions. The system was conceived and designed to establish effective, reliable autonomous operations, with automatic monitoring and recovery - minimizing human intervention while maintaining quality. We illustrate how far we have been able to achieve that.Comment: 13 pages, 9 figure

Structural Complexity and Decay in FLOSS Systems: An Inter-Repository Study

Past software engineering literature has firmly established that software architectures and the associated code decay over time. Architectural decay is, potentially, a major issue in Free/Libre/Open Source Software (FLOSS) projects, since developers sporadically joining FLOSS projects do not always have a clear understanding of the underlying architecture, and may break the overall conceptual structure by several small changes to the code base. This paper investigates whether the structure of a FLOSS system and its decay can also be influenced by the repository in which it is retained: specifically, two FLOSS repositories are studied to understand whether the complexity of the software structure in the sampled projects is comparable, or one repository hosts more complex systems than the other. It is also studied whether the effort to counteract this complexity is dependent on the repository, and the governance it gives to the hosted projects. The results of the paper are two-fold: on one side, it is shown that the repository hosting larger and more active projects presents more complex structures. On the other side, these larger and more complex systems benefit from more anti-regressive work to reduce this complexity

Achieving Cultural Fit in Global Information Systems Implementation

Designers and engineers that plan and manufacture technological systems imprint their values and practices onto these systems, without fully realizing that inconsistencies in cultural dimensions between developers and users may result in poor implementation of the new system due to resistance to change, among other causes. Therefore, manager\u27s awareness of cultural differences is a necessary condition in formulating GIS policies for implementation in different organizational settings across countries. The paper offers detailed examples of cultural differences between countries and their relations to the different stages of technology implementation, which may serve as a guideline for engineers, vendors, consultants, and managers of GIS interventions in formulating mechanisms for global implementation. Implementation managers are advised to adapt GIS to their own set of beliefs through the establishment of joint global and local teams, which represents all parties in the process. In this manner, rather than a cultural conflict, GIS implementation becomes a cultural exchange that reduces resistance to change

The Effect of Incorporating End-User Customization into Additive Manufacturing Designs

In the realm of additive manufacturing there is an increasing trend among makers to create designs that allow for end-users to alter them prior to printing an artifact. Online design repositories have tools that facilitate the creation of such artifacts. There are currently no rules for how to create a good customizable design or a way to measure the degree of customization within a design. This work defines three types of customizations found in additive manufacturing and presents three metrics to measure the degree of customization within designs based on the three types of customization. The goal of this work is to ultimately provide a consistent basis for which a customizable design can be evaluated in order to assist makers in the creation of new customizable designs that can better serve end-user. The types of customization were defined by doing a search of Thingiverse’s online data base of customizable designs and evaluating commonalities between designs. The three types of customization defined by this work are surface, structure, and personal customization. The associated metrics are used to quantify the adjustability of a set of online designs which are then plot against the daily use rate and each other on separate graphs. The use rate data used in this study is naturally biased towards hobbyists due to where the designs used to create the data resides. A preliminary analysis is done on the metrics to evaluate their correlation with design use rate as well as the dependency of the metrics in relation to each other. The trends between the metrics are examined for an idea of how best to provide customizable designs. This work provides a basis for measuring the degree of customization within additive manufacturing design and provides an initial framework for evaluating the usability of designs based on the measured degree of customization relative to the three types of defined customizations

Effects of Communication Protocol Stack Offload on Parallel Performance in Clusters

The primary research objective of this dissertation is to demonstrate that the effects of communication protocol stack offload (CPSO) on application execution time can be attributed to the following two complementary sources. First, the application-specific computation may be executed concurrently with the asynchronous communication performed by the communication protocol stack offload engine. Second, the protocol stack processing can be accelerated or decelerated by the offload engine. These two types of performance effects can be quantified with the use of the degree of overlapping Do and degree of acceleration Daccs. The composite communication speedup metrics S_comm(Do, Daccs) can be used in order to quantify the combined effects of the protocol stack offload. This dissertation thesis is validated empirically. The degree of overlapping Do, the degree of acceleration Daccs, and the communication speedup Scomm characteristic of the system configurations under test are derived in the course of experiments performed for the system configurations of interest. It is shown that the proposed metrics adequately describe the effects of the protocol stack offload on the application execution time. Additionally, a set of analytical models of the networking subsystem of a PC-based cluster node is developed. As a result of the modeling, the metrics Do, Daccs, and Scomm are obtained. The models are evaluated as to their complexity and precision by comparing the modeling results with the measured values of Do, Daccs, and Scomm. The primary contributions of this dissertation research are as follows. First, the metric Daccs and Scomm are introduced in order to complement the Do metric in its use for evaluation of the effects of optimizations in the networking subsystem on parallel performance in clusters. The metrics are shown to adequately describe CPSO performance effects. Second, a method for assessing performance effects of CPSO scenarios on application performance is developed and presented. Third, a set of analytical models of cluster node networking subsystems with CPSO capability is developed and characterised as to their complexity and precision of the prediction of the Do and Daccs metrics