A Study on System Availability Vs System Administration Efforts with Mathematical Models

Two mathematical models are developed in this paper to study the effectiveness of system administration efforts on the improvement of system availability, based on the assumption that there exists a transitional state for a computer system in operation before it is brought down by some hardware or software problems and with intensified system administration efforts, it is possible to discover and fix the problems in time to bring the system back to normal state before it is down. Markov chain is used to simulate the transition of system states. A conclusion is made that increasing system administration efforts may be a cost-effective way to meet the requirements for moderate improvement on system availability, but higher demand on this aspect still has to be met by advanced technologies.

Bridging reliability and operations management for superior system availability:Challenges and opportunities

Recently,firms have begun to handle the design,manufacturing,and maintenance of capital goods through a consolidated mechanism called the integrated product-service system.This new paradigm enables firms to deliver high-reliability products while lowering the ownership cost.Hence,holistic optimization models must be proposed for jointly allocating reliability,maintenance,and spare parts inventory across the entire value chain.In the existing literature,these decisions are often made fragmentally,thus resulting in local optimality.This study reviews the extant works pertaining to reliability-redundancy allocation,preventative maintenance,and spare parts logistics models.We discuss the challenges and opportunities of consolidating these decisions under an integrated reliability-maintenance-inventory framework for attaining superior system availability.Specific interest is focused on the new product introduction phase in which firms face a variety of uncertainties,including installed base,usage,reliability,and trade policy.The goal is to call for tackling the integrated reliability-maintenance-inventory allocation model under a nonstationary operating condition.Finally,we place the integrated allocation model in the semiconductor equipment industry and show how the firm deploys reliability initiatives and after-sale support logistics to ensure the fleet uptime for its global customers.

Modeling a Dynamic Data Replication Strategy to Increase System Availability in Cloud Computing Environments

Failures are normal rather than exceptional in the cloud computing environments. To improve system avai- lability, replicating the popular data to multiple suitable locations is an advisable choice, as users can access the data from a nearby site. This is, however, not the case for replicas which must have a fixed number of copies on several locations. How to decide a reasonable number and right locations for replicas has become a challenge in the cloud computing. In this paper, a dynamic data replication strategy is put forward with a brief survey of replication strategy suitable for distributed computing environments. It includes： 1） analyzing and modeling the relationship between system availability and the number of replicas; 2） evaluating and identifying the popular data and triggering a replication operation when the popularity data passes a dynamic threshold; 3） calculating a suitable number of copies to meet a reasonable system byte effective rate requirement and placing replicas among data nodes in a balanced way; 4） designing the dynamic data replication algorithm in a cloud. Experimental results demonstrate the efficiency and effectiveness of the improved system brought by the proposed strategy in a cloud.

Allocating redundancy,maintenance and spare parts for minimizing system cost under decentralized repairs

Reliability-redundancy allocation,preventive maintenance,and spare parts logistics are crucial for achieving system reliability and availability goal.Existing methods often concentrate on specific scopes of the system’s lifetime.This paper proposes a joint redundancymaintenance-inventory allocation model that simultaneously optimizes redundant component,replacement time,spares stocking,and repair capacity.Under reliability and availability criteria,our objective is to minimize the system’s lifetime cost,including design,manufacturing,and operational phases.We develop a unified system availability model based on ten performance drivers,serving as the foundation for the establishment of the lifetimebased resource allocation model.Superimposed renewal theory is employed to estimate spare part demand from proactive and corrective replacements.A bisection algorithm,enhanced by neighborhood exploration,solves the complex mixed-integer,nonlinear optimization problem.The numerical experiments show that component redundancy is preferred and necessary if one of the following situations occurs:extremely high system availability is required,the fleet size is small,the system reliability is immature,the inventory holding is too costly,or the handson replacement time is prolonged.The joint allocation model also reveals that there exists no monotonic relation between spares stocking level and system availability.

DESIGN FOR AVAILABILITY:A HOLISTIC APPROACH TO CREATE VALUE FOR MANUFACTURERS AND CUSTOMERS OF CAPITAL GOODS

This research introduces a holistic framework called Design for Availablhty that uses me principles of Lean Sigma and Design for X to cost-effectively optimize the availability of capital goods （i.e., technical systems used in the production of end-products or -services such as medical systems, airplanes, and manufacturing equipment） throughout their entire lifetime. Manufacturers require such a framework because users of capital goods increasingly insist on high system availability levels against reduced lifetime costs. The Design for Availability framework allows manufacturers to determine the current status of system availability and associated lifetime costs, and to identify opportunities to create additional value for themselves and their customers. A case study at a global manufacturer of capital goods in the food processing industry illustrates how the framework can be used in practice and to what extent the manufacturer and customers may profit from applying Design for Availability.