Considering the Energy Consumption of Mobile Storage Alternatives

This paper is motivated by a simple question: what are the energy consumption characteristics of mobile storage alternatives? To answer this question, we are faced with a large design space of multiple dimensions. Two important dimensions are the type of storage technologies and the type of file systems. In this paper, we systematically explore this large design space. We have constructed a logical disk system that can be easily configured to run on different storage technologies and to emulate the behavior of different file systems. As we explore the large number of configuration options made possible by this system, we gain many insights about the interaction between the device power management scheme and a log-structured design. This interaction is more complex than the conventional wisdom of equating performance and energy improvements. Instead, the most critical issue in determining the energy behavior is a complex interaction of three factors: the power management mechanism of the storage device, the distribution of the idleness in the workload, and the file system strategies that attempt to exploit and bridge these first two factors. As an example of the energy performance achieved on our implementation, a Microdrive running under a log-structured design consumes only 56% of the energy used by a comparable conventional system.