SUMMARY System virtualization has become the enabling technology to manage the increasing number of different applications inside data centers. The abstraction from the underlying hardware and the provision of multiple virtual machines (VM) on a single physical server have led to a consolidation and more efficient usage of physical servers. The abstraction from the hardware also eases the provision of applications on different data centers, as applied in several cloud computing environments. In this case, the application need not adapt to the environment of the cloud computing provider, but can travel around with its own VM image, including its own operating system and libraries. System virtualization and cloud computing could also be very attractive in the context of high‐performance computing (HPC). Today, HPC centers have to cope with both, the management of the infrastructure and also the applications. Virtualization technology would enable these centers to focus on the infrastructure, while the users, collaborating inside their virtual organizations (VOs), would be able to provide the software. Nevertheless, there seems to be a contradiction between HPC and cloud computing, as there are very few successful approaches to virtualize HPC centers. This work discusses the underlying reasons, including the management and performance, and presents solutions to overcome the contradiction, including a set of new libraries. The viability of the presented approach is shown based on evaluating a selected parallel, scientific application in a virtualized HPC environment. Copyright © 2011 John Wiley & Sons, Ltd.

Exponentially growing capacities of disk drives have increased the problem that not only a complete disk can fail, but also individual, small groups of sectors can be erroneous. These sector errors are especially critical during RAID rebuilds because they can only be detected when the corresponding sectors are read. Mechanisms to cope with sector errors, therefore, have become an important way to improve disk reliability. One approach to deal with sector errors is the introduction of intra-disk redundancy, where additional redundancy blocks are calculated and stored for each set of disk sectors. Previous studies have introduced intra-disk redundancy schemes and have evaluated their impact on disk reliability. None of these studies has evaluated the influence on disk drive performance or the underlying energy consumption. The study presented in this paper benchmarks existing schemes concerning these metrics. It shows the surprising result that weaker codes combined with newly introduced scrambling techniques can produce faster layouts with similar reliability properties than previously proposed strong codes.

The coordination between locomotion and respiration of Parkinson's disease (PD) patients is reduced or even absent. The degree of this disturbance is assumed to be associated with the disease severity [S. Schiermeier, D. Schäfer, T. Schäfer, W. Greulich, and M. E. Schläfke, "Breathing and locomotion in patients with Parkinson's disease," Eur. J. Physiol., vol. 443, No. 1, pp. 67-71, Jul. 2001]. To enable a long-term and online analysis of the locomotion-respiration coordination for scientific purpose, we have developed a distributed wireless communicating network. We aim to integrate biofeedback protocols with the real-time analysis of the locomotion-respiration coordination in the system to aid rehabilitation of PD patients. The network of sensor nodes is composed of intelligent network operating devices (iNODEs). The miniaturized iNODE contains a continuous data acquisition system based on microcontroller, local data storage, capability of on-sensor digital signal processing in real time, and wireless communication based on IEEE 802.15.4. Force sensing resistors and respiratory inductive plethysmography are applied for motion and respiration sensing, respectively. A number of experiments have been undertaken in clinic and laboratory to test the system. It shall facilitate identification of therapeutic effects on PD, allowing to measure the patients' health status, and to aid in the rehabilitation of PD patients.

Framework evolution may break existing users, which need to be migrated to the new framework version. This is a tedious and error-prone process that benefits from automation. Existing approaches compare two versions of the framework code in order to find changes caused by refactorings. However, other kinds of changes exist, which are relevant for the migration. In this paper, we propose to mine framework usage change rules from already ported instantiations, the latter being applications build on top of the framework, or test cases maintained by the framework developers. Our evaluation shows that our approach finds usage changes not only caused by refactorings, but also by conceptual changes within the framework. Further, it copes well with some issues that plague tools focusing on finding refactorings such as deprecated program elements or multiple changes applied to a single program element.

Storage Area Networks (SANs) connect groups of storage devices to servers over fast interconnects. An important challenge lies in managing the complexity of the resulting massive SAN configurations. Policy-based validation using new logical frameworks has been proposed earlier as a solution to this configuration problem. SANchk offers a new solution that uses standard technologies such as SQL, XML, and Java, to implement a rule-based configuration checker. SANchk works as a light-weight extension to the relational databases of storage management systems; current support includes IBM's TPC and the open source Aperi storage manager. Some five dozen best practices rules for SAN configuration are implemented in SANchk, many of them with configurable parameters. Empirical results with several commercial SANs show that the approach is viable in practice.

Storage area networks (SANs) connect groups of storage devices to servers over fast interconnects using protocols like Fibre Channel or iSCSI, so that storage resources can be assigned to servers in a flexible and scalable way. An important challenge is controlling the complexity of the SAN configuration resulting from the high scalability of the network and the diversity and the interconnectivity of the devices. Policy- based validation has been proposed earlier as a solution to this configuration problem. We propose a light-weight, SQL-based solution that uses existing well-known technologies to implement such a validation system. Our approach is based on a relational database which stores configuration data extracted from the system via a WBEM standard interface. In contrast to other approaches, we use SQL to define our policy rules as executable checks on these configuration data. Each rule is embedded in a test case, defined by an XML schema, which combines each check with an explanation component and an action component. These components retrieve information about the SAN components that cause the check to fail and provide methods that will be invoked on a success or a failure of the test. Although the approach is more general, we focus on the application for Storage Area Networks. We also give some example policies for SAN configuration and their implementations and show how in addition all policy types presented by Agrawal et al. (2004) can be formulated as SQL queries by our method.

In this paper, we discuss a set of functional requirements for software exploration tools and provide initial evidence that various combinations of these features are needed to effectively assist developers in understanding software. We observe that current tools for software exploration only partly support these features. This has motivated the development of SEXTANT, a software exploration tool tightly integrated into the Eclipse IDE that has been developed to fill this gap. By means of case studies, we demonstrate how the requirements fulfilled by SEXTANT are conducive to an understanding needed to perform a maintenance task

Current tools for software understanding mostly concentrate on one comprehension technique, e.g., visualization, or bottom-up navigation through software elements via hyperlinks. In this paper, we argue that to effectively assist developers in understanding today's software systems, a combination of several comprehension techniques is needed including seamless integration of top-down querying and bottom-up navigation strategies that work across different kinds of software artifacts; furthermore, application-domain and/or technology specific relationships between software elements should be taken into consideration; last but not least, a tight integration of such tools into development environments is crucial. We present SEXTANT, a software exploration tool tightly integrated into the Eclipse IDE that satisfies these requirements. In two case studies, we demonstrate how SEXTANT's features are conducive in tracking down the source of erroneous behavior, respectively, in discovering 'bad smells' in the software structure which should lead to code refactorings.