Flexible Fault Tolerance Research Articles

Modified Impedance-Source Inverter with Continuous Input Currents and Fault-Tolerant Operations

Impedance-source (Z-source) inverters are increasingly adopted in practice, where a high voltage gain is required. However, issues like drawing a non-continuous current from the DC source and ceasing the energy supply under DC source faults are also observed. In this paper, an embedded enhanced-boost Z-source inverter (EEB-ZSI) is thus proposed to tackle the issues. The proposed EEB-ZSI employs two DC sources, which enable the continuous input current and fault-tolerant operations (e.g., open-circuit and short-circuit faults in the DC sources). The operational principles are presented in detail with an in-depth circuit analysis. Moreover, the proposed EEB-ZSI is benchmarked with prior-art Z-source inverters. Experimental tests further demonstrate the effectiveness of EEB-ZSI regarding the continuous input current and flexible fault tolerance.

Flexible fault tolerance in cloud through replicated cooperative resource group

Fault tolerance (FT) is a highly focused issue in cloud due to high reliability requirements especially for delay sensitive tasks. Numerous FT frameworks in cloud have been proposed in literature. By and large, proactive and reactive FT approaches are followed in the existing frameworks. Irrespective of any of the applied approaches, FT implementation remains service provider centric in the existing frameworks. Cloud users are not given any control over deciding the level of FT. However, cloud follows the service orientation model with greater flexibility in using the computing services on demand basis and in pay-per-use manner. The user’s control in deciding the level of FT while executing their tasks will further reinforce the model of service orientation in cloud. Therefore, this paper proposes a flexible fault tolerance framework (FFTF) in cloud. FFTF provision the users to categorize their tasks as premium/standard/economy to implement the corresponding level of fault tolerance (FT). To implement a FT level, user task is executed on a cooperative resource group in cloud. Flexibility of FFTF is endorsed by maintaining the performance parameters of deadline guarantee ratio and average task delay for different task categories. The performance of FFTF is analyzed and compared through extensive simulation experiments on artificial and real workload in term of its FT capability, resource consumption and utilization with an existing FT framework.

Multigranulation sequential three-way decisions based on multiple thresholds

Three-way decisions have become a representative of trisecting-and-acting model for uncertainty data analysis. With granular computing point of view, a more reasonable decision-making model should process data from multiview and multilevel. Classical sequential three-way decisions are based on a granular structure with a single threshold under multiple levels of granularity, which make the traditional models incapable of adapting to the case of multiview granular structures with multiple thresholds. To overcome this disadvantage, we propose a generalized multigranulation sequential three-way decision model based on multiple different thresholds. By controlling the number of multiview granular structures satisfying the corresponding two tolerance thresholds, we further adopt the optimistic, pessimistic, variable, weighted and weighted arithmetic mean aggregation strategies to construct five kinds of multigranulation sequential three-way decision models from the quantitative point of view. The corresponding relationships and the uncertainty measures of these multigranulation sequential three-way decisions are discussed. Finally, the experimental results demonstrate that different multigranulation sequential three-way decisions can solve the problem under multiple granular structures and have more flexible fault tolerance under different levels of granularity. This study will enrich and prompt the development of the multigranulation three-way decisions.

A Flexibly Fault-Tolerant FU Array Processor and its Self-Tuning Scheme to Locate Permanently Defective Unit

Nowadays, small feature-sized transistors and wires led by the process miniaturization have shown increasing vulnerability to both transient and permanent faults. Modular redundancy in circuits and failure-unit isolation are thereby employed to guarantee the correct execution and also to well keep the lifespan of electronic devices. In this work, we propose the Explicit Redundancy Linear Array (EReLA) architecture to provide a highly flexible fault tolerance. EReLA follows the baseline reconfigurable architecture, which works best with failure-unit isolation and hot-swap techniques. In addition, specifically for the preparation of hot swaps, we propose a low-cost self-tuning scheme, to fast locate the precise position of the defective processing element or network connection. Powered by these schemes, EReLA is functionally the same as a traditional TMR processor in terms of fault tolerance, while the power data of a 180nm prototype EReLA chip has indicated that it incurs about 1/3 less power consumption than the TMR implementation.

A Flexible, Self-Tuning, Fault-Tolerant Functional Unit Array Processor

Today, small feature-sized transistors and wires led by process miniaturization have shown increasing vulnerability to both transient and permanent faults. Modular redundancy in circuits and failure-unit isolation are thereby employed to guarantee the correct execution and also to lengthen the lifespan of electronic devices. This article proposes the Explicit Redundancy Linear Array (EReLA) architecture to provide highly flexible fault tolerance. EReLA follows the baseline reconfigurable architecture, which works best with failure-unit isolation and hot-swap techniques. In addition, specifically for the preparation of hot swaps, the authors propose a low-cost self-tuning scheme to quickly locate the precise position of the defective processing element or network connection. Powered by these schemes, EReLA can function the same as a traditional TMR processor in terms of fault tolerance with a third less power consumption, as indicated by the power data of a 0.18 μm prototype EReLA chip. The simulation data indicates that EReLA achieves around 4× the lifespan of the traditional TMR processor.

Improving the fault resilience of an H.264 decoder using static analysis methods

Fault tolerance rapidly evolves into one of the most significant design objectives for embedded systems due to reduced semiconductor structures and supply voltages. However, resource-constrained systems cannot afford traditional error correction for overhead and cost reasons. New methods are required to sustain acceptable service quality in case of errors while avoiding crashes. We present a flexible fault-tolerance approach that is able to select correction actions depending on error semantics using application annotations and static analysis approaches. We verify the validity of our approach by analyzing the vulnerability and improving the reliability of an H.264 decoder using flexible error handling.

Flexible fault tolerance in distributed enterprise communities

We are witnessing the birth of the digital enterprise, in which many of the enterprise operations will be performed by independent software programs or by programs acting on behalf of humans. The agents are complex software entities, that should be able to maintain a state that survives failures. The classic solution is to use a relational database (such as Oracle), possibly replicated, to save the states of the agents in a manner that can survive failures and implement the communal invariants inside the database. In this paper we present a flexible, yet robust frame-work in which the interactions of the agents that work in a given community are governed by a given law that is enforced in a distributed manner. We provide several options to handle failures, maintaining the consistency of the states. The implementation is based on the distributed coordination and control mechanism called Law-Governed Interaction (LGI).

Quality-of-service-aware fault tolerance for grid-enabled applications

This study first reviews how grid-enabled applications can be provided with fault tolerance. Existing methods, implemented either in the grid application/middleware or in a Generalized Multi-Protocol Label Switching (GMPLS)-based network, are outlined. Then, the paper shows the advantages of integrating application/middleware fault-tolerant schemes, such as service replication, with GMPLS network-layer fault-tolerant schemes, such as path restoration. An integrated fault-tolerant scheme is capable of providing flexible QoS-aware fault tolerance while minimizing the necessary computational and network resources. In the end, the implementation of the proposed integrated scheme in a Video-on-Demand (VoD) application is experimentally validated.

Towards Nanoelectronics Processor Architectures

In this paper, we focus on reliability, one of the most fundamental and important challenges, in the nanoelectronics environment. For a processor architecture based on the unreliable nanoelectronic devices, fault tolerance schemes are required so as to ensure the basic correctness of any computation. Since any fault tolerance approach demands redundancy either in the form of time or hardware, reliability needs to be considered in conjunction with the performance and hardware tradeoffs. We propose a new computational model for the nanoelectronics based processor architectures, that provides flexible fault tolerance to deal with the high and time varying faults. The model guarantees the correctness of instruction executions, while dynamically balancing hardware and performance overheads. The correctness of every instruction is confirmed by multiple execution instances through a hybrid hardware-time redundancy approach. To achieve high system performance, multiple unconfirmed computation branches are exploited in a speculative manner. Hardware resource growth that these speculative computations entail is controlled so that the utilization of hardware is balanced between the two competing goals of performance and fault tolerance. In addition, we examine the impact on the proposed computational model of other nanoelectronic characteristics such as the necessity for localization of interconnections and the regularity of nanofabric structures on the proposed computational model. We set up an experimental framework to validate the effectiveness of the proposed scheme as well as to investigate multiple tradeoff points within the proposed approach. Simulation data confirm that the proposed computational model achieves the goal of providing flexible fault tolerance under a wide range of fault occurrence rates, while at the same time guaranteeing high system performance and efficient utilization of hardware resources.

Autonomic workflow execution in the grid

Mobile agents are being leveraged in both workflow management and grid computing contexts. The convergence of these two research streams supports execution in the grid where tasks are allowed to vary in their level of interdependence. The result is an expansion of grid applications beyond those which consist of homogeneous computations decomposed and performed in parallel to those which support the parallel execution of sequences of interdependent tasks that constitute a workflow. However, grid computation of critical workflows requires that the grid platform exhibits the autonomic characteristic of self-healing in order to ensure workflow execution. To address this issue, in this work, we first develop a model for dynamic fault tolerance technique selection, which can be embedded generically in a mobile agent workflow management system. We then augment an existing architecture for flexible fault tolerance in the grid with our model, thus allowing the system to optimally configure its fault tolerance mechanisms through awareness of the computational environment. The result is a foundation for autonomic workflow management in the grid

Distributed file management techniques based on an autonomous decentralized system concept

Distributed computer systems have been the subject of a large amount of research and development. From the standpoint of system construction and expansion, it is necessary that a computer system is flexible and tolerant enough for a change of system structure. A computer system is also required to be easily operated by users regardless of its structure and status. This paper presents techniques for file management in a distributed computer system to fulfil these requirements based on the Autonomous Decentralized System Concept. The proposed techniques achieve the autonomy of each computer unit and autonomous cooperation among these computer units in a distributed file system. These techniques realize flexible fault-tolerance of each file according to the degree of its importance. Additionally, one of the applications of the proposed techniques is also shown in this paper.

Triple redundant fault tolerance: A hardware-implemented approach

Our experience with the system described in this paper has shown that the HIFT design with distributed ASIC voters provides fault tolerance with extremely thorough and fast fault detection. We feel that the HIFT approach is far superior to software-implemented approaches, which require extensive and cumbersome software diagnostics to detect and isolate faults. Such software approaches tend not to have adequately high fault coverage and take longer to operate and detect faults than the HIFT approach. Furthermore, the controller's operating system has been kept simple and straightforward, lending itself to analysis, verification, and testing. The HIFT architecture also offers flexibility in extending the fault protection boundary beyond the controller itself. By using redundant input modules and guarded redundant output modules, the fault tolerant boundary can be extended to the process sensors and actuators. In summary, the HIFT approach provides high performance and flexible fault tolerance with minimal software complexity. This has yielded a design that meets our original goals of keeping the equipment simple to ensure the eits failure modes are understandable and controllable and that the system can be easily analyzed and maintained. In addition to meeting these goals, the design also provides: • ⊎ a very high degree of fault coverage, • ⊎ high-speed performance, • ⊎ tractable safety analysis, and • ⊎ simplified software feature upgrades and maintenance. A production prototype of the machine described in this paper was developed in April 1986, followed by eight months of environmental qualification testing and fault-injection testing. A beta test program was run from October, 1986 through May, 1987. Production unit deliveries began in June of 1987. Applications include electric power grid control, safety-critical process control, and emergency shutdown systems.

Flexible fault tolerance for distributed computer systems

Flexible fault tolerance for distributed computer systems