Software reliability and redundancy

Reliability, availability, and maintainability ram are three system attributes that are of tremendous interest to systems engineers, logisticians, and users. For a recent exam that i studied for, i asked myself this question. Basic fault tolerant software techniques geeksforgeeks. Mar 26, 2018 what is the difference between redundancy and replication in software. An inadequate level of reliability may determine the commercial failure of a software product. It can be formally defined as 1 down time total time100%.

Software reliability is a key part in software quality. We shall address these issues in our future research as well. Software reliability modeling has matured to the point that meaningful results can be obtained by applying suitable models to the problem. These innovative tools offer solutions for a wide range of reliability and related modelling and analysis techniques, such as life data analysis. In reliability engineering one way to get high plant and equipment reliability is to provide an extra unit that is available to immediately replace the duty unit when it fails. Keys to software reliability are not only structure and care in design implementation, and verification of software, but also effective use of redundancy in the form of robust data structure and information about what constitutes expected behaviour of the software 17. Understanding the difference between reliability and availability. Mar 14, 20 hardware redundancy is achieved by providing two or more physical copies of a hardware component. Software reliability cmuece carnegie mellon university. Active redundancy an overview sciencedirect topics. Bqr is a world leader in eda electronic design automation, rams reliability, availability, maintainability and safety and ils integrated logistic support software and professional services. Nevertheless, despite the commitment and the rigorous verification processes employed by developers, software is deployed with faults.

Reliability, availability and serviceability wikipedia. Simply browse and select your primary and secondary opc servers. In other words, the software does fail often but it recovers quickly, thereby having less impact on system availability. High availability is a high percentage of time that the system is functioning. The software offers a sophisticated graphical interface that allows you to model the simplest or most complex systems and processes using reliability block diagrams rbds or fault tree analysis fta or a combination of both approaches. Opc redundancy free redundancy software opc expert. Taking advantage microsoft windows nt robustness and including features for redundancy in the software are key challenges for pcbased control in factoryfloor automation. Combining all analysis techniques in one complete package fmea, fracas, fault tree, reliability prediction, rbd, maintainability prediction, weibull, and alt relyence studio offers the unique advantage of encompassing all your. The previous example used a subsystem with a failure probability of 0. Understanding the difference between reliability and. The models are subject of studies in reliability and safety engineering. The reliability of the overall system is then calculated by treating units 1 and 2 as one unit with a reliability of 98.

Software reliability and availability software engineering. A modified form of software redundancy, applied to hardware may be. Do not affect software reliability, except it may affect program inputs. The principle objective of applying redundancy is achieve reliability goals. The study of software reliability can be categorized into three parts. A key attribute of dependability is the reliability of the system, so that the rendered service is available throughout its operating duration at an acceptable performance level. Both resilience and redundancy are critical for the design and. Dependability is the facet of reliability that relates to the degree of certainty that a relay or relay system will operate, or perform, correctly. Software reliability an overview sciencedirect topics.

It is a reasonable guess that every large piece of software that has ever been produced has contained faults bugs. Reliability block diagrams of system elements are developed and employed. Software reliability characteristics can be estimated using the procedures provided in this notebook. When other techniques, such as use of more reliable components, manufacturing quality control, test, design simplification, etc. Redundancymaster is a dropin application that does not require you to make any changes to your opc client or server applications. Redundancy is the presence of different elements with the same functionality. Sep 10, 2019 redundancy is an absolute measure of the additional components supporting system resilience, whereas resiliency is a relative and continuous measure of the impact of fault on the system operation. Reliability block diagram analysis rbd analysis reliasoft. Basics of traditional reliability carnegie mellon university. When youre designing your network or updating it to increase reliability, one thing you should build into everything is redundancy. To increase the reliability of software systems, researchers have investigated the use of various form of redundancy. Software and solutions for reliability and maintainability analysis. Alternatively, analytical methods can also be used to perform these. Four of the computers, each loaded with identical software, operate in what is termed the redundant set during critical mission phases such as ascent and descent.

In this paper we discuss intrinsic software redundancy, a type of redundancy that. Hardware vs software reliabilitya comparative study. Its intuitive configuration takes only minutes and will allow you to easily establish a redundant opc system. There are probably a variety of reasons for this omission, including the additional cost and time. Reliability must be built into the project from the start. The software reliability optimization problem will be formulated into a mixedinteger programming problem. System reliability can be modeled at a component level, assuming the failure rate is constant exponential distribution. Redundancy is the installation of additional or alternate network devices, communication mediums or equipment in your infrastructure. Software reliability is the probability that the software will execute for a particular period of time without failure, weighted by the cost to the user of each failure encountered. Redundancy is a common approach to improve the reliability and availability of a system. Each redundant pair seamlessly appears as a single opc server to any opc client application. Redundancymaster increases the reliability and availability of your opc data by allowing multiple opc servers to be configured into redundant pairs.

High levels of reliability can be predicted and achieved as far as the hardware portions of modern large and complex realtime computerbased control systems are concerned but software is a critical part and plays a vital role in influencing the overall system reliability. Software interfaces are purely conceptual other than visual. The input and output transducers have fairly high availability, thus fairly high availability can be achieved even without redundant components. Nearly all businesses are moving data and applications apps from their own data centers and systems to cloud based softwareasaservice.

We briefly discussed tier level and redundancy standards. A software system is redundant when it performs the same. Redundancy to increase the reliability of software systems, various forms of redundancy are used. Collectively, they affect economic lifecycle costs of a system and its utility. Faulttolerant software assures system reliability by using protective redundancy at the software level. What is the difference between redundancy and replication in software. Software failures are mostly due to the activation of design faults by specific input sequences. These failures are function failure and reliability failure. The k outof n configuration is a special case of parallel redundancy.

Informally, a software system is redundant when it performs the same functionality through the execution of different elements. In the previous article, you may recall simple definitions and descriptions of data center redundancy levels and design. Opc expert software has opc redundancy built in to help increase the reliability and availability of opc servers. Understanding the difference between reliability and availability people often confuse reliability and availability. Can not improve software reliability if identical software components are used. Reliability, availability and serviceability, also known as reliability, availability, and maintainability, is a computer hardware engineering term involving reliability engineering, high availability, and serviceability design. Even extremely experienced software engineers make so many mistakes that for improving the reliability of software each task must be carried out in a redundant manner. A good software development plan is a key aspect of the software reliability program.

Reliasoft blocksim provides a comprehensive platform for system reliability, availability, maintainability and related analyses. Redundancy models can account for failures of internal system components and therefore change the effective system reliability and availability performance. They must have an understanding of design, the software system, what hardware is used and its factors of reboots and a sense of the redundancy in order to determine what needs to be done to meet reliability and availability requirements. Both resilience and redundancy help achieve a systems dependability, but they are not interchangeable strategies. This type of configuration requires that at least components.

Hardware redundancy an overview sciencedirect topics. Software reliability and redundancy optimization ieee conference. Both schemes are based on software redundancy assuming that the events of coincidental software failures are rare. Also tests extensions must be related with tests profile and correctness i a. Continual process and cpu data exchange creates redundancy to ensure system reliability. Redundant system basic concepts national instruments. Reliability and redundancy in production management. Reliasoft reliability and maintainability analysis reliasoft. Common cause failures occur when the redundant subsystems have correlated or. Dec 01, 2017 engineer just right reliability engineers need to be knowledgeable in all aspects of the product. Software reliability emerged in the early 1970s and was created to predict the number of defects or faults in software as a method of measuring software quality.

Software reliability is also an important factor affecting system reliability. Its five generalpurpose computers have reliability through redundancy, rather than the expensive quality control employed in the apollo program 61. There are two basic techniques for obtaining faulttolerant software. Bqr offers software tools that enhance, improve and optimize engineering processes in order to save costs and bring better, more robust products to. In engineering, redundancy is the duplication of critical components or functions of a system.

Software redundancy for simatic s7 function manual, 042010, a5e0217156502 9 software redundancy and operator stations with wincc faceplate for operating and monitoring tasks page 97 configuring the faceplate using wincc page 99 configuring the connection for wincc page 67 defining the faceplate tags page 100. What is the difference between redundancy and replication in. A common reliability metric is the number of software. At first i thought they were the same, but given a little more thought there was a. System reliability and availability calculations bmc blogs.

A key attribute of dependability is the reliability of the system, so that the. Different forms of redundant design are the core technology of wellestablished reliability and fault tolerant mechanisms in traditional engineering as well as in software engineering. Redundancy has been extensively exploited in many software engineering techniques, for example for faulttolerance and reliability. Single version techniques aim to improve the fault tolerance of a software component by adding to it mechanisms for fault detection, containment, and recovery. Redundancy is the existence of more than one means for performing a given function. A software reliability tocost relation is developed both from a software reliability related cost model and software redundancy models with commoncause failures. Software reliability optimization by redundancy and software. The phrase was originally used by international business machines as a term to describe the robustness of their mainframe computers.

High availability software is software used to ensure that systems are running and available most of the time. A software reliability engineer has to be a computer scientist and be very. A variety of online tools and calculators for system reliability engineering, including redundancy calculators, mtbf calculators, reliability prediction for electrical and mechanical components, simulation tools, sparing analysis tools, reliability growth planning and tracking, reliability calculators for probability distributions, weibull analysis and maintainability analysis calculations. Design for reliability is a collection of techniques that are used to modify the initial design of a system to improve its reliability. Handling software faults with redundancy the imdea software. The third approach to reduce the number of defects in software is the introduction of redundancy when developingsoftware. In xenon, xen cards handle the call processing for digital trunks connected to the xen cards. The cost of reliability in general, reliable systems take the slow, steady route. Software reliability cannot be predicted from any physical basis since it depends entirely on human factors in design. Furthermore, hyper data centers and new technologies like software defined networking sdn are changing the value of redundancy.

System reliability models and redundancy techniques in system design table of contents s. Individual hardware platforms and the software assigned to those platforms. The main reason is that software has a much lower mttr. Redundancy is all about delivering the highest levels of reliability. It cannot improve software reliability if identical software elements are used. Software reliability optimization by redundancy and. Software engineering software failure mechanisms javatpoint. In practice, other redundancy strategies such as a koutofn structure may be used see, e. A process for reliability related quality programming is developed to fill existing gaps in software design and development so that a quality programming plan can be achieved. Software features blocksim supports an extensive array of reliability block diagram rbd configurations and fault tree analysis fta gates and events, including advanced capabilities to model complex configurations, load sharing, standby redundancy, phases and duty cycles. The configuration of the second unit can be as a standby, or as a redundancy, or as a backup. Functional failure is observed from the start of product life, and it is caused by production or raw material defect. Business continuity planning assumptions are changing the way companies recover from impact scenarios and minimize the disruption to. In software, redundancy is useful and used in many ways, for example for fault tolerance and reliability engineering.

A reliability block diagram rbd may be used to demonstrate the interconnection between individual components. Functional capabilities of computer system components encompass hardware, software, information, and timebased performance. Simply put availability is a measure of the % of time the equipment is in an operable state while reliability is a measure of how long the item performs its intended function. Software reliability is the probability of failurefree software operation for a specified period of time in a specified environment. Redundancy has been extensively exploited in many software engineering techniques, for example for faulttolerance and. Testing, verification, modelimplementation comparison typically add one. Business continuity planning assumptions are changing the way companies recover from impact scenarios and minimize the disruption to daily. Abstract software redundancy is an essential mechanism in engineering.

Computers designed with higher levels of ras have many features that protect data integrity and help them stay available for long periods. Engineer just right reliability engineers need to be knowledgeable in all aspects of the product. This software option is a custom function block, residing in the valve, designed specifically for redundancy. Therefore, to guarantee high levels of reliability in the presence of faults, software systems must be designed to reduce the impact of the failures caused by such.

In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the form of a backup or failsafe, or to improve actual system performance, such as in the case of gnss receivers, or multithreaded computer processing. For redundant, fault tolerant systems, software recovery characteristics are system design and implementation dependent. Software redundancy is used mainly against software failures. What is the difference between redundancy and replication. Department of defense dod contractors do not fully exploit these techniques. The multidisciplinary nature of embedded systems demand an all encompassing approach to reliability, requiring consideration of traditional hardware reliability, as well as software and mechanical reliability. Topics in software reliability material drawn from somerville, mancoridis. Reliability, availability and serviceability ras, also known as reliability, availability, and maintainability ram, is a computer hardware engineering term involving reliability engineering, high availability, and serviceability design. Reliability, availability, and maintainability sebok.

Adding redundancy increases the cost and complexity of a system design and with the high reliability of modern electrical and mechanical components, many applications do not need redundancy in order to be successful. It differs from hardware reliability in that it reflects the design perfection, rather than manufacturing perfection. Blocksim rbds, fault trees and markov diagrams reliasoft. The difference between standby, backup, redundancy in. This makes the reliability of a software module dependent on the. Reliability failure is observed after usage over period of time. Traditional reliability carnegie mellon university 18849b dependable embedded systems spring 1998 author. Costoriented task allocation and hardware redundancy. There are two types of software fault tolerance techniques.