Mobile virtualization introduces extra layers in software stacks, which leads to performance degradation. Especially, each I/O operation has to pass through several software layers to reach the NAND-flash-based storage systems. This paper targets at optimizing I/O for mobile virtualization, since I/O becomes one of major performance bottlenecks that seriously affects the performance of mobile devices. Among all the I/O operations, a large percentage is updating metadata. Frequent updating metadata not only degrades overall I/O performance but also severely reduces flash memory lifetime. In this paper, we propose a novel I/O optimization techniqueto identify the metadata of a guest file system which is storedin a VM (Virtual Machine) image file and frequently updated. Then, these metadata are stored in a small additional NVM(Non-Volatile Memory) which is faster and more endurableto greatly improve flash memory's performance and lifetime. To the best of our knowledge, this is the first work to identifythe file system metadata from regular data in a guest OS VMimage file under mobile virtualization. The proposed schemeis evaluated on a real hardware embedded platform. Theexperimental results show that the proposed techniques canimprove write performance to 45.21% in mobile devices withvirtualization.