MobiSys 2004: Second International Conference on Mobile Systems, Applications, and Services, June, 2004, Boston, USA
  MobiSys Home   Organizers   Invitation   Tech Session   Registration  
  Workshops   Poster/Demo/Video   Authors/Speakers   Hotel/Travel   Invitation to Student Volunteer Program  

Mimic: Raw Activity Shipping for File Synchronization in Mobile File Systems

Tae-Young Chang, Aravind Velayutham, and Raghupathy Sivakumar, Georgia Institute of Technology

In this paper, we consider the problem of file synchronization when a mobile host shares files with a backbone file server in a network file system. Previous schemes proposed to improve upon the transfer overheads of full file transfer based synchronization approaches are based on the diff or dirty block approach. In such schemes, file system blocks that have either been changed, or newly introduced, with respect to the old copy at the server are identified and selectively transferred. However, we show that for most common applications, the magnitude of changes in the file's structure predominantly lacks any correlation to the magnitude of changes actually made to its contents, chiefly due to application specific storage semantics. For such applications, diff based schemes effectively reduce to a full file transfer approach. In this context, we motivate the need for an approach that can incur transfer overheads proportional to the magnitude of user level changes, but at the same time remains application unaware. We then propose an application independent approach that relies on transferring user activity records to the server, where the new file is recreated through a playback of the user activity on the old copy of the file. The proposed approach relies on a combination of schemes including user activity to file mapping, intelligent recording, fast playback, and file verification to perform the synchronization efficiently. Finally, we identify conditions under which diff based approaches do perform better than the proposed approach, but show that detection of such conditions is straightforward thus enabling both schemes to be used in tandem with a mobile file system for bandwidth-efficient file synchronization.