I. Introduction
Nowadays, the amount of data collected from a great variety of sources, which have already been massive, are still growing at an explosive rate. This urges current file systems to provide effective but also efficient services for data storage and retrieval. However, one of the critical challenges faced by file service providers is that they often have to contain duplicate copies of file contents as data are being accumulated. Typical real-world examples can be easily found in increasingly popular Internet social applications, such as Facebook, Youtube and Twitter etc., where file duplication occurs with a high frequency when users share and synchronize files between each other. As unfavourable consequences, the limited storage space is redundantly consumed and the network bandwidth is wasted.