Constructing a risk dependency-based availability model

Information flow and business workflow within an organization are close related. While organizational information infrastructures becomes more and more complex, disasters or accidents usually cause serious damages and losses to organizations and individuals, sometimes even force companies to withdraw from markets. Hence, many organizations consider disaster recovery as an important issue regarding to their business continuity managements. Disaster recovery allows an organization restore its business from consequences of various accidents. However, the consequences of an accident on a system usually depend on the statuses of systems interconnected to the system. While evaluating system risks, interdependent systems should be considered together. Usually under cost constrains, organizations seldom adopt N-to-N schemes while implementing their backup systems. In this paper, we propose a system backup model based on risk dependency considering overall availability of interconnected mutual backup systems. There are four types of interdependencies in information systems, fully dependent, partially dependent, multiple dependent and indirect dependent will be defined. The overall availability of systems with fundamental interconnection topologies, serial connection and parallel connection, will also be discussed and calculated in detail.