Nowadays, Android has been widely installed in mobile devices, including smart-phones, tablet PCs, and PMPs, that are equipped with a wealth of standard capabilities, such as touchpad display, wireless communications, GPS, and memory-based storage. In Android systems, most users perform many activities not only phone calls, but also internet browsing, emailing, playing games, taking and sharing pictures, downloading and reading mobile e-books, and using multimedia applications. These activities and user responsiveness are mainly affected by Android IO subsystems since the Android framework uses many IO operations with framework components. In Android-based systems, IO subsystems are organized with both internal system storage and external data storage. We analyze storage traffic of three android killer applications, Gallery, Web browsing, and SNS services, by profiling storage IO for various user activities. Based on this analysis, we summarize the statistical pattern of various Android applications, and show the effect of the proposed IO write buffering scheme which reduces the number of writes for the storage system and increases latency.