Low-energy standby-sparing for hard real-time systems

Time-redundancy techniques are commonly used in real-time systems to achieve fault tolerance without incurring high energy overhead. However, reliability requirements of hard real-time systems that are used in safety-critical applications are so stringent that time-redundancy techniques are sometimes unable to achieve them. Standby sparing as a hardwareredundancy technique can be used to meet high reliability requirements of safety-critical applications. However, conventional standby-sparing techniques are not suitable for lowenergy hard real-time systems as they either impose considerable energy overheads or are not proper for hard timing constraints. In this paper we provide a technique to use standby sparing for hard real-time systems with limited energy budgets. The principal contribution of this work is an online energymanagement technique which is specifically developed for standby-sparing systems that are used in hard real-time applications. This technique operates at runtime and exploits dynamic slacks to reduce the energy consumption while guaranteeing hard deadlines. We compared the low-energy standby-sparing (LESS) system with a low-energy timeredundancy system (from a previous work). The results show that for relaxed time constraints, the LESS system is more reliable and provides about 26% energy saving as compared to the time-redundancy system. For tight deadlines when the timeredundancy system is not sufficiently reliable (for safety-critical application), the LESS system preserves its reliability but with about 49% more energy consumptio

تقدير وثوقية نظام توليد الطاقة الكهربائية

تقدم هذه الورقة مدخلاً عاماً من أجل تحديد نموذج ماركوف للأنظمة المحييّطة، والذي على أساسه تم تحديد نموذج ماركوف للوثوقية من أجل محطات التوليد المزودة بوحدات توليد احتياطية جاهزة (احتياطي ساخن، ظاهر أو سري) redundant standby aparent or secret سواء كانت هذه الوحدات قابلة للإصلاح أو غير قابلة الإصلاحreparable or non- reparable. وأخيرا تم تقديم تحليل  كمي لوثوقية محطات التوليد المزودة بالاحتياطي المذكور redundant standby  في كل من حالة النظام القابل للصيانة وحالة النظام غير القابل للصيانة، بحيث يظهر أثر الصيانات على رفع وثوقية محطات التوليد المذكورة.   In this paper, a general approach to establishing the Markov reliability model of the redundant systems is presented. On the basis of this approach, the Markov reliability model of generating stations is determined, which are watered with non-repairable or repairable standby redun­dant generating units. Finally, a quantitative reliability analysis of the two-component standby redundant units generating station is per­formed. The analysis indicates that repairing has a very significant influence on the reliability increase of these stations

Estimation of Reliability Parameters of a Complex Repairable System

In this paper estimation of reliability parameters of a complex repairable system is considered and semi-markov process is used in analyzing various reliability parameters such as Transition Probabilities, Mean sojourn times, MTSF, Availability and Busy period of repairman in repairing the failed units. In the past, Arora et-al[2] has done reliability analysis of two unit standby redundant system with constrained repair time. Gupta et-al [6] has worked on a compound redundant system involving human failure. Rander et-al [2] has evaluated the cost analysis of two dissimilar cold standby systems with preventive maintenance and replacement of standby units. A pioneer work in this field was done by Gopalan [1] and Osaki [3] by performing analysis of warm standby system and parallel system with bivariate exponential life respectively. Earlier, Pathak et al [7&8] studied reliability parameters of a main unit with its supporting units and also compared the results with two different distributions. In this paper, Chapman-Kolmogorov equations are used to develop recursive relations. Also the involvement of preventive maintenance in the model increases the reliability of the functioning units. In the end a particular case is also taken for discussion

Expert System for UNIX System Reliability and Availability Enhancement

Highly reliable and available systems are critical to the airline industry. However, most off-the-shelf computer operating systems and hardware do not have built-in fault tolerant mechanisms, the UNIX workstation is one example. In this research effort, we have developed a rule-based Expert System (ES) to monitor, command, and control a UNIX workstation system with hot-standby redundancy. The ES on each workstation acts as an on-line system administrator to diagnose, report, correct, and prevent certain types of hardware and software failures. If a primary station is approaching failure, the ES coordinates the switch-over to a hot-standby secondary workstation. The goal is to discover and solve certain fatal problems early enough to prevent complete system failure from occurring and therefore to enhance system reliability and availability. Test results show that the ES can diagnose all targeted faulty scenarios and take desired actions in a consistent manner regardless of the sequence of the faults. The ES can perform designated system administration tasks about ten times faster than an experienced human operator. Compared with a single workstation system, our hot-standby redundancy system downtime is predicted to be reduced by more than 50 percent by using the ES to command and control the system

Reliability and Availability of Ship’s Computer Systems Based on Manufacturer’s Data and Worksheets

Computer controlled systems play important role aboard ships. Failure of such systems due to some component malfunction can be with fatal consequences. It is important to assess reliability and availability of such systems and minimum redundancy to ensure maintenance planning, ordering of spare components and safety of the voyage with as little as possible redundant components. This paper deals with development of model for reliability and availability of the computer system, which consists of three components with hot standby. Markov chains model is used to analyse probability of failure. Matrix of transitions is set after model development. Transition matrix is used to develop differential equations for model simulation. System’s reliability is larger if the system is under constant maintenance and service, but it would not be available. Hence, the optimum between reliability and availability should be found. System’s maintenance is limited during the voyage and hot standby is necessary to ensure success of the voyage. This paper presents a framework for assessment of reliability and availability of computer systems based on components’ redundancy, and practical data about MTBF. Many versions of the shipboard computer systems can be evaluated using the presented framework

Evaluation of reliability parameters of a system having three independent components with repair facility

Barlow & Prochan [1] were first to study a complex system taking the component failure and repair times as Independent of each other. In recent years, many papers on reliability such as Li  [2] used multi-state weighted k- out- of- n systems to analyze repairable systems with arbitrary failure time distributions. Exponential distribution plays an important role in the study of system with repair. In order to predict and  estimate or optimize the probability of survival and the mean life, it is essential to take exponential distribution.  Earlier, Goel et al[8 ] have done similar reliability analysis taking units in three different modes. Rander et-al [6] has evaluated the cost analysis of two dissimilar cold standby systems with preventive maintenance and replacement of standby units. A pioneer work in this field was done by Gopalan [3] and Osaki [5] by performing analysis of warm standby system and parallel system with bivariate exponential life respectively. Earlier, Pathak et al [10 & 11] studied reliability parameters of a main unit with its supporting units and also compared the results with two different distributions. We define semi-up mode as the case when the one particular unit is not able to operate due to error in other units which makes these units non-operative. In this paper an attempt has been made by authors by incorporating the concept of semi-up mode and tried to obtain the reliability parameters of working system taking three independent components.&nbsp

PREDICTIVE RELIABILITY ANALYSIS OF REDUNDANT SHIP NAVIGATIONAL RADAR SYSTEM

U radu je predstavljen opći pristup uspostavljanju Markovljeva modela pouzdanosti redundantnih sustava. Na temelju tog pristupa uspostavljen je Markovljev model pouzdanosti neobnovljivog i obnovljivog dvokomponentnog standby redundantnog sustava. Nadalje, obavljena je kvantitativna komparativna analiza pouzdanosti dvokomponentnog standby redundantnog brodskog navigacijskog radarskog sustava. Analiza pokazuje da obnavljanje sustava značajno utječe na porast njegove pouzdanosti.In this paper, a general approach to establishing the Markov reliability model of the redundant system is presented. On the basis of this approach, the Markov reliability model of non-repairable and repairable two-component standby redundant systems is established. Finally, a quantitative comparative reliability analysis of the two-component standby redundant ship navigational radar system is performed. The analysis indicates that repairing has a very significant influence on the reliability increase of this system

Recovery From Node Failure in Distributed Query Processing

While distributed query processing has many advantages, the use of many independent, physically widespread computers almost universally leads to reliability issues. Several techniques have been developed to provide redundancy and the ability to recover from node failure during query processing. In this survey, we examine three techniques--upstream backup, active standby, and passive standby--that have been used in both distributed stream data processing and the distributed processing of static data. We also compare several recent systems that use these techniques, and explore which recovery techniques work well under various conditions