EEPC: Energy-Efficient Persistent Cache Scheme for Mobile Distributed File Systems

For mobile distributed file systems (MDFSs), files can be easily shared among multiple mobile devices. However, it requires the connected remote devices to be online all the time for timely file browsing, which incurs significant energy consumption. This is unacceptable for battery-powered mobile devices. To address this issue, we propose EEPC, an energy-efficient persistent cache scheme for MDFSs. It consists of several techniques. First, a proactive cache invalidation mechanism is designed to ensure optimistic access to the local persistent cache, which greatly reduces unnecessary read requests. Second, a lazy cache synchronization policy is designed to reorganize writeback requests, which ensures that remote devices remain in a low-power state for a long time. Finally, a cache admission and eviction scheme is proposed, which considers both file access frequency and recency, and an adaptable file prefetching scheme is adopted to quickly recover invalidated cache files. Evaluations on real devices show that EEPC maintains at least 60% of sleep time for remote devices and greatly extends the interval between two wake-ups, regardless of the frequency of remote file accesses. Compared with the state-of-the-art, the energy consumption of remote devices can be reduced by 33.6%, on average.