Analyzing, modeling and evaluating dynamic adaptive fault tolerance strategies in cloud computing environments

Currently, using commercial off-the-shelf (COTS) components and constructing parallel system becomes the main way to improve satellite system performance remarkably. System reliability relying on its structure rather than devices makes system fault-tolerant architecture and strategy increasingly important. As centralized fault-tolerant solution has the inherent drawback of single point of failure (SPOF), it can not guarantee system reliability well. Distributed fault- tolerant method, due to its complexity and large overhead, has not been maturely used. In this paper, we propose a new distributed fault-tolerant scheme with high reliability and flexibility, in which an equal symmetric distributed fault- tolerant (ESDFt) architecture is constructed. Based on the structure, functional module framework of system nodes and autonomous fault-tolerant strategy are designed. The ESDFt scheme creates favorable conditions for flexible implementation of system fault tolerance. It utilizes the master election mechanism, which eliminates the risks of SPOF and chooses master node intelligently based on user's configuration, making fault-tolerant complexity and processing overhead flexibly adjustable. The verification and evaluation of ESDFt scheme has been performed on a prototype system. The experiment results prove that ESDFt scheme not only ensures system reliability well, but also enhances system flexibility and practicality at the same time.

Recent technological advances in digital signal processing, data compression techniques, and high-speed communication networks have made Video-on-Demand (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a VOD server requires a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Furthermore, due to real-time constraints, the reliability requirements of VOD systems are even more stringent than those of traditional information systems. Traditional RAID solutions are inadequate due to poor resource usage. Thus, in this paper, we present alternative schemes which provide a high degree of reliability at low disk storage, bandwidth, and memory costs for on-demand multimedia servers. Moreover, we discuss some of the main issues and trade-offs associated with providing fault tolerance in multidisk VOD systems. We would like to impress upon the reader that one of the main points of this paper is the exposition of trade-offs and issues associated with designing fault-tolerant VOD servers. It is not the case that one fault tolerance scheme is absolutely better than another, but rather that one must understand the trade-offs as well as one's system constraints and then choose a fault tolerance scheme accordingly.

This paper develops a modulation based fault-tolerant (FT) strategy for restoring the operation of three-phase modular multilevel converters (MMCs) with faulty switches. This FT strategy is based on a proposed modified space vector modulation (SVM) technique that generates balanced line-to-line (line) voltages even in the case of a fault occurrence. In the postfault operation, the proposed strategy is able to restore the fundamental amplitude of the line to the neutral (load) voltages to that of the normal operation condition with a slightly increased voltage stress over the switches in the faulty phase. In this paper, first a brief background about MMCs and SVM technique is provided. Then, the proposed FT strategy and the modified SVM technique are presented. Finally, several simulation and experimental results are provided to validate operation of the proposed strategy.

Due to modern technology trends such as decreasing feature sizes and lower voltage levels, fault tolerance (FT) is becoming increasingly important in computing systems. Several schemes have been proposed to enable a user to configure the FT at the application level, thereby enabling the user to trade stronger FT for performance or vice versa. In this paper, we propose supporting instruction-level rather than application-level configurability of FT, since different parts of some applications (e.g., multimedia) can have different reliability requirements. Weak or no FT will be applied to less critical parts, resulting in time and/or resource gains. These gains can be used to apply stronger FT techniques to the more critical parts; hence increasing the overall reliability. The paper shows how some existing FT techniques can be adapted to support instruction-level FT configurability, how a programmer can specify the desired FT level of the instructions, and how the compiler can manage it automatically. A comparison between the existing FT scheme EDDI (which duplicates all instructions) and the proposed approach is performed both at the kernel and at full application levels. The simulation results show that both the performance and the energy consumption are significantly improved (up to 50% at the kernel and up to 16% at full application level), while the fault coverage depends on the application. For the full application (JPEG encoder), our approach is only applied to one kernel in order to avoid increasing the programming effort significantly.

Fault tolerance is an important requirement for long-running parallel programs. This paper presents a different approach to fault-tolerance support in message-passing parallel programs based on their structural and behavioral characteristics, commonly known as patterns. A classification of these patterns and their applicable fault-tolerance strategies is aimed to facilitate an application developer to incorporate appropriate fault-tolerance strategies to an application. Fault-tolerance strategies for two of the patterns are discussed, and one specific strategy is elaborated and analyzed. The presented strategies have been incorporated into a fault-tolerance support framework called FT-PAS. One objective of the framework is to separate the fault tolerance related details from an application developer's main objectives (separation-of-concerns). The paper presents the additional key features of the framework, and concludes with a discussion on current and future research directions.

Fault tolerant system based on non-integers order observers: Application in a heat exchanger

Special Issue on Software and Systems Reuse in the Big Data Era

This paper focuses on insufficient perception in blind scenes and the failures of the actuator and sensor of vehicle suspension. The safe speed is designed and the fault-tolerant strategy based on the observer is designed when the actuator and sensor fail simultaneously. A speed planning strategy to ensure that vehicles operate at a safe speed is proposed. The Markov suspension fault jump model considering the suspension sensor and actuator faults is established. Based on the fault estimation obtained by the fault observer, a fault tolerance control strategy of sensor signal reconstruction and actuator fault compensation is adopted. The measurement index for evaluating fault tolerance effectiveness has been established, and an exploration of fault tolerance control is conducted across various fault levels, to identify the preferred fault tolerance strategies corresponding to different levels of fault tolerance. The simulation results show that the designed speed control strategy can improve vehicle safety by decelerating in advance, the fault observer is capable of accurately estimating the true values of actuator and sensor faults. The simulation and vehicle test results demonstrate that similar suspension performance has been obtained by fault-tolerant control strategy and preferred fault tolerance under different fault tolerance levels compared with normal fault tolerance.

This paper investigates the power management and fault tolerance in DVS-enabled real-time systems based on the EDF scheme. The power management is achieved via dynamic voltage scaling DVS and fault tolerance is achieved via checkpoint scheme. We estimate a critical speed which effectively decreases the energy consumption by the associated frequency dependent and independent devices. The proposed low power fault tolerance scheduling scheme includes two parts: 1 an offline solution to compute the optimal number of checkpoints and the running speed; 2 an online speed reduction mechanism based on the actual workload by using the slack time. The experimental results show that the proposed approach which is compared to the previous method Melhem et al., 2004 significantly reduces the energy consumption.

Vehicle data management with specific wear-levelling and fault tolerance for hybrid DRAM-NVM memory

User-directed means the process of carrying out fault tolerance is dynamic and the fault tolerance mode is chosen by users based on application requirements. In this paper, we introduce a general scheme based on standard MPI to provide the user directed support for application level algorithmic fault tolerance. The user-directed fault tolerance plays the role as a connection between applications and algorithmic fault tolerance. As a case study, our scheme has been incorporated to HPL combined with a non-blocking ABFT technique. We have tested the functional availability of our scheme for fault tolerance in real circumstance. We also evaluated that when there is no failure occurring, our support only brings 2.5 percent overhead. When failure occurs, with our scheme, the scalability of algorithmic fault tolerance maintains well.

Due to the poor accessibility, poor operating conditions, high failure rate, long maintenance time, and difficult maintenance of wind hybrid generators, the economic loss is huge once the failure stops. To this end, the fault adaptive fault-tolerant control of distributed wind and wind hybrid generators is studied, the historical operation data of offshore wind and wind hybrid generators and onshore wind and wind hybrid generators are counted and compared, and the fault characteristics of key components of offshore wind and wind hybrid generators are analyzed. The generator sets are summarized, and the common electrical faults of wind turbines and their impacts on the system are analyzed. This paper summarizes the current research status of fault-tolerant operation of existing offshore wind and wind complementary generators in terms of software fault tolerance and hardware fault tolerance, summarizes the current fault tolerance schemes for offshore wind and wind complementary generators, and analyzes the application feasibility of existing fault tolerance schemes. In addition, the main problems of fault-tolerant offshore wind and solar complementary generator sets are pointed out, and future research hotspots are foreseen.

Fault tolerance (FT) is a topic of major concern in achieving dependable systems, for both real time as well as non real time systems. The paper provides a model of achieving fault tolerance, based on the ISO/ITU Reference Model for Open Distributed Processing (RM-ODP). This reference model provides a system software engineering methodology for fault tolerance, an object based model of fault tolerance, system requirements for achieving fault tolerance in an open manner, modeling constructs and rules to enable a proper system specification of fault tolerance, and business rules in terms of policies to achieve a well formed system specification. All these aspects are discussed at some depth, but the author primarily focuses on how certain behavior can be specified and achieved in an object based system, the constructs of the Unified Modeling Language (UML) and the Object Constraint Language (OCL).

This paper discusses fault tolerance in discrete-time dynamic systems, such as finite-state controllers or computer simulations, with focus on the use of coding techniques to efficiently provide fault tolerance to linear finite-state machines (LFSMs). Unlike traditional fault tolerance schemes, which rely heavily-particularly for dynamic systems operating over extended time horizons-on the assumption that the error-correcting mechanism is fault free, we are interested in the case when all components of the implementation are fault prone. The paper starts with a paradigmatic fault tolerance scheme that systematically adds redundancy into a discrete-time dynamic system in a way that achieves tolerance to transient faults in both the state transition and the error-correcting mechanisms. By combining this methodology with low-complexity error-correcting coding, we then obtain an efficient way of providing fault tolerance to k identical unreliable LFSMs that operate in parallel on distinct input sequences. The overall construction requires only a constant amount of redundant hardware per machine (but sufficiently large k) to achieve an arbitrarily small probability of overall failure for any prespecified (finite) time interval, leading in this way to a lower bound on the computational capacity of unreliable LFSMs.

Given that the reliability of a very large-scaled system is inversely related to the number of computing elements, fault tolerance has become a major concern in high performance computing including the most recent deployments with graphic processing units (GPUs). Many fault tolerance strategies, such as the checkpoint/restart mechanism, have been studied to mitigate failures within such systems. However, fault tolerance mechanisms generate additional costs and these may cause a significant performance drop if it is not used carefully. This paper presents a novel fault tolerance scheduling model that explores the interplay between the GPGPU application performance and the reliability of a large GPU system. This work focuses on the checkpoint scheduling model that aims to minimize fault tolerance costs. Additionally, a GPU performance analysis is conducted. Furthermore, the effect of a checkpoint/restart mechanism on the application performance is thoroughly studied and discussed.