Standby System Reliability through DRBD

The standby approach is of strategic importance in current technologies, since it is able to reduce the environmental impact while extending the system lifetime, allowing to achieve a trade-off among dependability properties and costs. This is particularly interesting in the IT context where the acquired awareness on energy efficiency and environmental issues pushed towards new forms and paradigms of ("green") computing to specifically address such aspects. Standby policies, mechanisms and techniques are characterized by complex phenomena that should be adequately investigated. This need is translated in a strong demand of adequate tools for standby system modelling and evaluation. In this paper the dynamic reliability block diagrams (DRBD) formalism, extending RBD to the representation of dynamic reliability aspects, is proposed for adoption in the standby system evaluation. In order to fill this gap, the DRBD semantics is revised to cover the specific peculiarities of standby system. Then, the effectiveness of the DRBD approach in standby modelling is demonstrated through a case study on a critical area surveillance system, where a capacity planning parametric analysis is performed to design the system through warm standby redundant cameras according to specific reliability requirements.