Overview of Mobile File Systems Presented by Steve Todd For WSU CS 898T Mobile and Wireless Networks Class 5/3/04

Introduction n Present overview of mobile file systems n Present several characteristics that complicate file system operation for mobile applications n Present overview of Coda - How Coda deals with these complications

Mobile File Systems n Allow mobile users to run applications that access shared files over a mobile network n Applications behave the same regardless of where user is located n Act as middleware between operating system and application

Mobile vs. Stationary n Resources for mobile devices never more than for stationary devices n Mobility inherently hazardous n Mobile device network connectivity highly variable in reliability and performance n Mobile devices dependent on a finite energy source

Autonomy vs. Interdependence n Balance between autonomy and interdependence necessary for optimal system performance n Adaptability = main goal of mobile file systems (compromise)

Mobile File Systems Characteristics n Provide location transparency n Provide replication (optimistic/pessimistic) n Provide cache consistency n Provide connected and disconnected operational modes n Provide scalability

MFS Modes of Operation

Coda Distributed File System n Files grouped into volumes replicated on Coda servers n Version stamping to resolve conflict n Client caching reduces network dependence and provides scalability n Uses optimistic approach n Callbacks to maintain cache coherency

Coda Client File Session

Coda Client States

Conclusions n Data consistency, data caching, scalability, location transparency, data replication, and availability n Adaptability to network

References Satyanarayanan, M. Fundamental Challenges in Mobile Computing. Fifteenth ACM Symposium on Princ. of Distr. Comp. May n Honeyman, P., Huston, L. B. Communications and Consistency in Mobile File Systems. IEEE Personal Communications, Dec. 1995, pp n Braam, P. J. The Coda Distributed File System. Carnegie Mellon University. n Schiller, J. Mobile Communications (2 nd ed.). Addison-Wesley, 2003, pp n Tanenbaum, A. S., van Steen, M. Distributed Systems: Principles and Paradigms. Prentice Hall, 2002, pp