Using DRBD in the Design of Redundant Distributed Computing System

Sustainability, environmental issues, low-carbon economy, are increasingly impacting on both research and technologies, attracting the attention on energy management issues. New challenges and requirements arise from them and have to match with existing (functional and non-functional) ones as well as with costs. In particular, the IT area has been hit by this "new wave", pushing towards new forms of ("green") computing paradigms to specifically address such aspects. In this scenario, standby policies and techniques can play a key role, able to implement a trade-off among dependability, energy efficiency and cost requirements. However, they are characterized by complex phenomena that should be adequately investigated, especially from a dependability perspective, calling for specific 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 the gap between the demand and actual solutions, 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.