Department of Computer Science , UTSA Technical Report : CS - TR - 2007 - 001 Energy Efficient Redundant Configurations for Reliable Servers in Distributed Systems ∗

Modular redundancy and temporal redundancy are traditional techniques to increase system reliability. In addition to being used as temporal redundancy, with technology advancements, slack time can also be used by energy management schemes to save energy. In this paper, we consider the combination of modular and temporal redundancy to achieve energy efficient reliable service provided by multiple servers. We first propose an efficient adaptive parallel recovery scheme that appropriately processes service requests in parallel to increase the number of faults that can be tolerated and thus system reliability. Then we explore schemes to determine the optimal redundant configurations of the parallel servers to minimize system energy consumption for a given reliability goal or to maximize system reliability for a given energy budget. Our analysis shows that small requests, optimistic approaches, and parallel recovery favor lower levels of modular redundancy, while restricted large requests, pessimistic approaches and serial recovery favor higher levels of modular redundancy. ∗A preliminary version of the paper appeared in EDCC 2005.