Quantitative assessment of the level of computer systems dependability

Abstract

This article discusses the issues of present interest of quantitative assessment of the level of computer systems dependability. A proposed method allows having obtained the numerical values of the dependability of system levels of the system under study, to analyze the system under study, as well as decide on the preference of a particular implementation variant of the system dependability. For this purpose, an attribute model of the computer systems dependability (AMD) is presented, which is based on the basic properties (attributes) of dependable computer systems (DCS) and on the metrics of these properties. The definitions of basic attributes and metrics, their calculated and qualitative characteristics are given. The problem of formalization of a generalized criterion of the level of achievement of the dependability system performance is solved. A formalized criterion for assessing the level of dependability, which is a linear functional, is proposed. Each attribute of the dependable system is considered as a set of metrics that can be measured by computational, experimental, or expert methods. On the basis of quantitative estimates of metrics, quantitative estimates of attributes are calculated which makes it possible to calculate quantitative estimates of the achieved level of dependability of the system under consideration for various variants of its implementation. The above criterion also takes into account the weighting factors of the influence of attributes and metrics of the system under study. Quantitative estimates of the level of performance of metrics are relative values, normalized to the required in the specification or limit values. On the basis of a simplified example, the calculation of the quantitative assessment of the level of computer system dependability is demonstrated. On the basis of the given example, it is shown how to obtain the numerical value of the level of system dependability under study. The described method of calculation allows analyzing detailed the values of the levels of dependability of various options for the implementation of the investigated CS, and to make reasoned conclusions about the advantages of one system being created over another.