Showing papers on "Redundancy (engineering) published in 2012"

Lateral Collinearity and Misleading Results in Variance-Based SEM: An Illustration and Recommendations

Abstract: Variance-based structural equation modeling is extensively used in information systems research, and many related findings may have been distorted by hidden collinearity. This is a problem that may extent to multivariate analyses in general, in the field of information systems as well as in many other fields. In multivariate analyses, collinearity is usually assessed as a predictor-predictor relationship phenomenon, where two or more predictors are checked for redundancy. This type of assessment addresses vertical, or “classic,” collinearity. However, another type of collinearity may also exist, called here “lateral” collinearity. It refers to predictor-criterion collinearity. Lateral collinearity problems are exemplified based on an illustrative variance-based structural equation modeling analysis. The analysis employs WarpPLS 2.0, with the results double-checked with other statistical analysis software tools. It is shown that standard validity and reliability tests do not properly capture lateral collinearity. A new approach for the assessment of both vertical and lateral collinearity in variance-based structural equation modeling is proposed and demonstrated in the context of the illustrative analysis.

Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA)

Abstract: This paper presents an overview of motor drive technologies used for safety-critical aerospace applications, with a particular focus placed on the choice of candidate machines and their drive topologies. Aircraft applications demand high reliability, high availability, and high power density while aiming to reduce weight, complexity, fuel consumption, operational costs, and environmental impact. New electric driven systems can meet these requirements and also provide significant technical and economic improvements over conventional mechanical, hydraulic, or pneumatic systems. Fault-tolerant motor drives can be achieved by partitioning and redundancy through the use of multichannel three-phase systems or multiple single-phase modules. Analytical methods are adopted to compare caged induction, reluctance, and PM motor technologies and their relative merits. The analysis suggests that the dual (or triple) three-phase PMAC motor drive may be a favored choice for general aerospace applications, striking a balance between necessary redundancy and undue complexity, while maintaining a balanced operation following a failure. The modular single-phase approach offers a good compromise between size and complexity but suffers from high total harmonic distortion of the supply and high torque ripple when faulted. For each specific aircraft application, a parametrical optimization of the suitable motor configuration is needed through a coupled electromagnetic and thermal analysis, and should be verified by finite-element analysis.

The bliss (not the problem) of motor abundance (not redundancy).

Abstract: Motor control is an area of natural science exploring how the nervous system interacts with other body parts and the environment to produce purposeful, coordinated actions. A central problem of motor control – the problem of motor redundancy – was formulated by Nikolai Bernstein as the problem of elimination of redundant degrees-of-freedom. Traditionally, this problem has been addressed using optimization methods based on a variety of cost functions. This review draws attention to a body of recent findings suggesting that the problem has been formulated incorrectly. An alternative view has been suggested as the principle of abundance, which considers the apparently redundant degrees-of-freedom as useful and even vital for many aspects of motor behavior. Over the past ten years, dozens of publications have provided support for this view based on the ideas of synergic control, computational apparatus of the uncontrolled manifold hypothesis, and the equilibrium-point (referent configuration) hypothesis. In particular, large amounts of “good variance” – variance in the space of elements that has no effect on the overall performance – have been documented across a variety of natural actions. “Good variance” helps an abundant system to deal with secondary tasks and unexpected perturbations; its amount shows adaptive modulation across a variety of conditions. These data support the view that there is no problem of motor redundancy; there is bliss of motor abundance.

Design and Control of a Modular Multilevel HVDC Converter With Redundant Power Modules for Noninterruptible Energy Transfer

Abstract: This paper presents design and control methods for fault-tolerant operations with redundant converter modules, one of the most prominent features in modular multilevel converter (MMC) topology. In fully implementing MMC functionalities, a nearest level control is applied as a low-switching modulation method. A dual sorting algorithm is newly proposed for effectively reducing the switching commutations of each power module as well as for voltage balancing control. Built upon these primary MMC topological and control features, its redundant operation is comprehensively investigated for fail-safe energy transfer. In particular, a novel spare process is proposed to handle an emergency situation when the number of faulty power modules exceeds the module redundancy. Since topological redundancy may cause the switching commutations of power modules in an arm to be unevenly distributed, a practical and effective mitigation measure is incorporated to keep the energy balance while avoiding the undesired switching stresses. Rigorous simulation studies for MMC and its application for high-voltage direct current are performed to demonstrate the validity and effectiveness of the proposed spare process under normal and emergency conditions.

Detection and correction of silent data corruption for large-scale high-performance computing

Abstract: Faults have become the norm rather than the exception for high-end computing clusters. Exacerbating this situation, some of these faults remain undetected, manifesting themselves as silent errors that allow applications to compute incorrect results. This paper studies the potential for redundancy to detect and correct soft errors in MPI message-passing applications while investigating the challenges inherent to detecting soft errors within MPI applications by providing transparent MPI redundancy. By assuming a model wherein corruption in application data manifests itself by producing differing MPI messages between replicas, we study the best suited protocols for detecting and correcting corrupted MPI messages. Using our fault injector, we observe that even a single error can have profound effects on applications by causing a cascading pattern of corruption which in most cases spreads to all other processes. Results indicate that our consistency protocols can successfully protect applications experiencing even high rates of silent data corruption.

Characteristics of backup workloads in production systems

Abstract: Data-protection class workloads, including backup and long-term retention of data, have seen a strong industry shift from tape-based platforms to disk-based systems. But the latter are traditionally designed to serve as primary storage and there has been little published analysis of the characteristics of backup workloads as they relate to the design of disk-based systems. In this paper, we present a comprehensive characterization of backup workloads by analyzing statistics and content metadata collected from a large set of EMC Data Domain backup systems in production use. This analysis is both broad (encompassing statistics from over 10,000 systems) and deep (using detailed metadata traces from several production systems storing almost 700TB of backup data). We compare these systems to a detailed study of Microsoft primary storage systems [22], showing that backup storage differs significantly from their primary storage workload in the amount of data churn and capacity requirements as well as the amount of redundancy within the data. These properties bring unique challenges and opportunities when designing a disk-based filesystem for backup workloads, which we explore in more detail using the metadata traces. In particular, the need to handle high churn while leveraging high data redundancy is considered by looking at deduplication unit size and caching efficiency.

Base-station assisted device-to-device communications for high-throughput wireless video networks

Abstract: We propose a new scheme for increasing the throughput of video files in cellular communications systems. This scheme exploits (i) the redundancy of user requests as well as (ii) the considerable storage capacity of smartphones and tablets. Users cache popular video files and — after receiving requests from other users — serve these requests via device-to-device localized transmissions. We investigate what is the optimal collaboration distance, trading off frequency reuse with the probability of finding a requested file within the collaboration distance. We show that an improvement of spectral efficiency of one to two orders of magnitude is possible, even if there is not very high redundancy in video requests.

ERSA: Error Resilient System Architecture for Probabilistic Applications

Abstract: There is a growing concern about the increasing vulnerability of future computing systems to errors in the underlying hardware. Traditional redundancy techniques are expensive for designing energy-efficient systems that are resilient to high error rates. We present Error Resilient System Architecture (ERSA), a robust system architecture which targets emerging killer applications such as recognition, mining, and synthesis (RMS) with inherent error resilience, and ensures high degrees of resilience at low cost. Using the concept of configurable reliability, ERSA may also be adapted for general-purpose applications that are less resilient to errors (but at higher costs). While resilience of RMS applications to errors in low-order bits of data is well-known, execution of such applications on error-prone hardware significantly degrades output quality (due to high-order bit errors and crashes). ERSA achieves high error resilience to high-order bit errors and control flow errors (in addition to low-order bit errors) using a judicious combination of the following key ideas: 1) asymmetric reliability in many-core architectures; 2) error-resilient algorithms at the core of probabilistic applications; and 3) intelligent software optimizations. Error injection experiments on a multicore ERSA hardware prototype demonstrate that, even at very high error rates of 20 errors/flip-flop/108 cycles (equivalent to 25000 errors/core/s), ERSA maintains 90% or better accuracy of output results, together with minimal impact on execution time, for probabilistic applications such as K-Means clustering, LDPC decoding, and Bayesian network inference. In addition, we demonstrate the effectiveness of ERSA in tolerating high rates of static memory errors that are characteristic of emerging challenges related to SRAM Vccmin problems and erratic bit errors.

Reliability and Availability Evaluation of Wireless Sensor Networks for Industrial Applications

Abstract: Wireless Sensor Networks (WSN) currently represent the best candidate to be adopted as the communication solution for the last mile connection in process control and monitoring applications in industrial environments. Most of these applications have stringent dependability (reliability and availability) requirements, as a system failure may result in economic losses, put people in danger or lead to environmental damages. Among the different type of faults that can lead to a system failure, permanent faults on network devices have a major impact. They can hamper communications over long periods of time and consequently disturb, or even disable, control algorithms. The lack of a structured approach enabling the evaluation of permanent faults, prevents system designers to optimize decisions that minimize these occurrences. In this work we propose a methodology based on an automatic generation of a fault tree to evaluate the reliability and availability of Wireless Sensor Networks, when permanent faults occur on network devices. The proposal supports any topology, different levels of redundancy, network reconfigurations, criticality of devices and arbitrary failure conditions. The proposed methodology is particularly suitable for the design and validation of Wireless Sensor Networks when trying to optimize its reliability and availability requirements.

Design and Analysis of an Integral Sliding Mode Fault-Tolerant Control Scheme

Abstract: A novel scheme for fault-tolerant control is proposed in this paper, in which integral sliding mode ideas are incorporated with control allocation to cope with the total failure of certain actuators, under the assumption that redundancy is available in the system. The proposed scheme uses the effectiveness level of the actuators to redistribute the control signals to healthy actuators without reconfiguring the controller. The effectiveness of the proposed scheme against faults or failures is tested in simulation based on a large transport aircraft model.

Network storage systems having clustered raids for improved redundancy and load balancing

Abstract: A clustered network-based storage system includes a host server, multiple high availability system controller pairs, and multiple storage devices across multiple arrays. Two independent storage array subsystems each include a quorum drive copy and are each controlled by a HA pair, with remote volume mirroring links coupling the separate HA pairs. The host server includes a virtualization agent that identifies and prioritizes communication paths, and also determines capacity across all system nodes. A system storage management agent determines an overall storage profile across the system. The virtualization agent, storage management agent, quorum drive copies and remote volume mirroring link all operate to provide increased redundancy, load sharing, or both between the separate first and second arrays of storage devices.

A Unified Approach to Reliability Assessment of Multiphase DC–DC Converters in Photovoltaic Energy Conversion Systems

Abstract: A systematic framework for reliability assessment and fault-tolerant design of multiphase dc-dc converters deployed in photovoltaic applications is presented. System-level steady-state models allow a detailed specification of component failure rates, and in turn establish the effects of ambient conditions and converter design on reliability. Markov reliability models are derived to estimate the mean time to system failure. Case studies applied to two- and three-phase, 250-W converters demonstrate that topological redundancy does not necessarily translate to improved reliability for all choices of switching frequency and capacitance. Capacitor voltage rating is found to be the dominant factor that affects system reliability.

Fault-Tolerant Design Considerations and Control Strategies for Aerospace Drives

Abstract: This paper considers existing more electric technologies in commercial aircraft and observes modern reliability data and redundancy techniques to highlight the reasons restricting the application of new components featuring electric drives and electromechanical actuation. Two techniques for maintaining a constant torque when faulted are applied to two very different fault-tolerant drives. Taking into consideration the test results and reliability data, conclusions are drawn as to the suitability of these and other drive configurations with regard to the stringent aerospace reliability and fault tolerance standards.

LDPC convolutional codes using layered decoding algorithm for high speed coherent optical transmission

Abstract: We successfully realized layered decoding for LDPC convolutional codes designed for application in high speed optical transmission systems. A relatively short code with 20% redundancy was FPGA-emulated with a Q-factor of 5.7dB at BER of 10−15.

Throughput-sensitive redundancy encoding schemes for data storage

Abstract: Techniques for optimizing data storage are disclosed herein. In particular, methods and systems for implementing redundancy encoding schemes with data storage systems are described. The redundancy encoding schemes may be scheduled according to system and data characteristics. The schemes may span multiple tiers or layers of a storage system. The schemes may be generated, for example, in accordance with a transaction rate requirement, a data durability requirement or in the context of the age of the stored data. The schemes may be designed to rectify entropy-related effects upon data storage. The schemes may include one or more erasure codes or erasure coding schemes. Additionally, methods and systems for improving and/or accounting for failure correlation of various components of the storage system, including that of storage devices such as hard disk drives, are described.

Combining Partial Redundancy and Checkpointing for HPC

Abstract: Today's largest High Performance Computing (HPC) systems exceed one Petaflops (10^15) floating point operations per second) and exascale systems are projected within seven years. But reliability is becoming one of the major challenges faced by exascale computing. With billion-core parallelism, the mean time to failure is projected to be in the range of minutes or hours instead of days. Failures are becoming the norm rather than the exception during execution of HPC applications. Current fault tolerance techniques in HPC focus on reactive ways to mitigate faults, namely via checkpoint and restart (C/R). Apart from storage overheads, C/R-based fault recovery comes at an additional cost in terms of application performance because normal execution is disrupted when checkpoints are taken. Studies have shown that applications running at a large scale spend more than 50% of their total time saving checkpoints, restarting and redoing lost work. Redundancy is another fault tolerance technique, which employs redundant processes performing the same task. If a process fails, a replica of it can take over its execution. Thus, redundant copies can decrease the overall failure rate. The downside of redundancy is that extra resources are required and there is an additional overhead on communication and synchronization. This work contributes a model and analyzes the benefit of C/R in coordination with redundancy at different degrees to minimize the total wall clock time and resources utilization of HPC applications. We further conduct experiments with an implementation of redundancy within the MPI layer on a cluster. Our experimental results confirm the benefit of dual and triple redundancy -- but not for partial redundancy -- and show a close fit to the model. At ~80,000 processes, dual redundancy requires twice the number of processing resources for an application but allows two jobs of 128hours wall clock time to finish within the time of just one job without redundancy. For narrow ranges of processor counts, partial redundancy results in the lowest time. Once the count exceeds ~770,000, triple redundancy has the lowest overall cost. Thus, redundancy allows one to trade-off additional resource requirements against wall clock time, which provides a tuning knob for users to adapt to resource availabilities.

Exploiting redundancy in Cartesian impedance control of UAVs equipped with a robotic arm

Abstract: A Cartesian impedance control for UAVs equipped with a robotic arm is presented in this paper. A dynamic relationship between generalized external forces acting on the structure and the system motion, which is specified in terms of Cartesian space coordinates, is provided. Through a suitable choice of such variables and with respect to a given task, thanks to the added degrees of freedom given by the robot arm attached to the UAV, it is possible to exploit the redundancy of the system so as to perform some useful subtasks. The hovering control of a quadrotor, equipped with a 3-DOF robotic arm and subject to contact forces and external disturbances acting on some points of the whole structure, is tested in a simulated case study.

System, apparatus, and method supporting asymmetrical block-level redundant storage

Abstract: A block-level storage system and method support asymmetrical block-level redundant storage by automatically determining performance characteristics associated with at least one region of each of a number of block storage devices and creating a plurality of redundancy zones from regions of the block storage devices, where at least one of the redundancy zones is a hybrid zone including at least two regions having different but complementary performance characteristics selected from different block storage devices based on a predetermined performance level selected for the zone. Such "hybrid" zones can be used in the context of block-level tiered redundant storage, in which zones may be intentionally created for a predetermined tiered storage policy from regions on different types of block storage devices or regions on similar types of block storage devices but having different but complementary performance characteristics. The types of storage tiers to have in the block-level storage system may be determined automatically, and one or more zones are automatically generated for each of the tiers, where the predetermined storage policy selected for a given zone is based on the determination of the types of storage tiers.

Consolidating Speech Recognition Results

Abstract: Candidate interpretations resulting from application of speech recognition algorithms to spoken input are presented in a consolidated manner that reduces redundancy. A list of candidate interpretations is generated, and each candidate interpretation is subdivided into time-based portions, forming a grid. Those time-based portions that duplicate portions from other candidate interpretations are removed from the grid. A user interface is provided that presents the user with an opportunity to select among the candidate interpretations; the user interface is configured to present these alternatives without duplicate elements.

Split-attention and redundancy effects on mobile learning in physical environments

Abstract: This study investigated split-attention and redundancy effects in a mobile learning environment on leaf morphology of plants as a function of different combinations of media. Eighty-one fifth-grade students were randomly assigned to the following three conditions: texts with pictures embedded in the mobile device (TP condition); texts embedded in the mobile device and real objects that are outside of the mobile device (TO condition); and texts with pictures embedded in the mobile device and real objects that are outside of the mobile device (TPO condition). Differences in performance on comprehension tests and learning efficiency were examined across conditions. The TP condition was expected to perform better than the TO condition due to a split-attention effect. The TP and TO conditions were expected to perform better than the TPO condition due to a redundancy effect. The results indicated no difference between the TP and the TO condition in comprehension and learning efficiency, but the TP and TO conditions performed better than the TPO condition on both measures. The implications of the results for research and design of mobile learning environments are discussed.

Low-cost program-level detectors for reducing silent data corruptions

Abstract: With technology scaling, transient faults are becoming an increasing threat to hardware reliability. Commodity systems must be made resilient to these in-field faults through very low-cost resiliency solutions. Software-level symptom detection techniques have emerged as promising low-cost and effective solutions. While the current user-visible Silent Data Corruption (SDC) rates for these techniques is relatively low, eliminating or significantly lowering the SDC rate is crucial for these solutions to become practically successful. Identifying and understanding program sections that cause SDCs is crucial to reducing (or eliminating) SDCs in a cost effective manner. This paper provides a detailed analysis of code sections that produce over 90% of SDCs for six applications we studied. This analysis facilitated the development of program-level detectors that catch errors in quantities that are either accumulated or active for a long duration, amortizing the detection costs. These low-cost detectors significantly reduce the dependency on redundancy-based techniques and provide more practical and flexible choice points on the performance vs. reliability trade-off curve. For example, for an average of 90%, 99%, or 100% reduction of the baseline SDC rate, the average execution overheads of our approach versus redundancy alone are respectively 12% vs. 30%, 19% vs. 43%, and 27% vs. 51%.

TSV Redundancy: Architecture and Design Issues in 3-D IC

Abstract: 3-D technology provides many benefits including high density, high bandwidth, low-power, and small form-factor. Through Silicon Via (TSV), which provides communication links for dies in vertical direction, is a critical design issue in 3-D integration. Just like other components, the fabrication and bonding of TSVs can fail. A failed TSV can severely increase the cost and decrease the yield as the number of dies to be stacked increases. A redundant TSV architecture with reasonable cost is proposed in this paper. Based on probabilistic models, some interesting findings are reported. First, the number of failed TSVs in a tier is usually less than 2 when the number of TSVs in a tier is less than 1000 and less than 5 when the number of TSVs in a tier is less than 10000. Assuming that there are at most 2-5 failed TSVs in a tier. With one redundant TSV allocated to one TSV block, our proposed structure leads to 90% and 95% recovery rates for TSV blocks of size 50 and 25, respectively. Finally, analysis on overall yield shows that the proposed design can successfully recover most of the failed chips and increase the yield of TSV to 99.4%.

Storage system, storage control apparatus, and storage control method

Abstract: A storage system including first storage devices constituting a first logical storage area, second storage devices constituting a second logical storage area; and a storage control apparatus. The storage control apparatus manages the first and second logical storage areas so that the data stored in the first and second logical storage areas have redundancy, and parity data for the data stored in the second logical storage area are stored in parity storage areas arranged in part of the second storage devices. When part of the first storage devices constituting part of the first logical storage area fail, the storage control apparatus generates part of the data stored, before the failure, in the part of the first storage devices, and stores the generated part of the data in at least part of the second parity storage areas in the second logical storage area.

Reliability Analysis of Nonrepairable Cold-Standby Systems Using Sequential Binary Decision Diagrams

Abstract: Many real-world systems, particularly those with limited power resources, are designed with cold-standby redundancy for achieving fault tolerance and high reliability. Cold-standby units are unpowered and, thus, do not consume any power until needed to replace a faulty online component. Cold-standby redundancy creates sequential dependence between the online component and standby components; in particular, a standby component can start to work and then fail only after the online component has failed. Traditional approaches to handling the cold-standby redundancy are typically state-space-based or simulation-based or inclusion/exclusion-based methods. Those methods, however, have the state-space explosion problem and/or require long computation time particularly when results with a high degree of accuracy are desired. In this paper, we propose an analytical method based on sequential binary decision diagrams (SBDD) for combinatorial reliability analysis of nonrepairable cold-standby systems. Different from the simulation-based methods, the proposed approach can generate exact system reliability results. In addition, the system SBDD model and reliability evaluation expression, once generated, are reusable for the reliability analysis with different component failure parameters. The approach has no limitation on the type of time-to-failure distributions for the system components or on the system structure. Application and advantages of the proposed approach are illustrated through several case studies.

Applying Network Theory to Quantify the Redundancy and Structural Robustness of Water Distribution Systems

Abstract: A water distribution system, represented as a spatially organized graph, is a complex network of multiple interconnected nodes and links. The overall robustness of such a system, in addition to the reliability of individual components, depends on the underlying network structure. This paper presents a deterministic network-based approach to study the relationship between the structure and function of water distribution systems and to critically review the application of structural measurements in the analysis of vulnerability and robustness of such systems. Benchmark water supply networks are studied, and their level of resistance to random failures and targeted attacks on their bridges and cut-sets are explored. Qualitative concepts such as redundancy, optimal connectivity, and structural robustness are quantified. Among other measurements, two metrics of meshedness coefficient and algebraic connectivity are found of great use toward quantifying redundancy and optimal connectivity, respectively. A brief ...