Redundancy is the traditional technique used to increase system reliability. With modern technology, in addition to being used as temporal redundancy, slack time can also be used by energy management schemes to scale down system processing speed and supply voltage to save energy. In this paper, we consider a system that consists of multiple servers for providing reliable service. Assuming that servers have self-detection mechanisms to detect faults, we first propose an efficient parallel recovery scheme that processes service requests in parallel to increase the number of faults that can be tolerated and thus the system reliability. Then, for a given request arrival rate, we explore the optimal number of active severs needed for minimizing system energy consumption while achieving k-fault tolerance or for maximizing the number of faults to be tolerated with limited energy budget. Analytical results are presented to show the trade-off between the energy savings and the number of faults being tolerated.
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