Overview of Mobile File Systems

1
Overview of Mobile File Systems

• Presented by Steve Todd
• For WSU CS 898T Mobile and Wireless Networks
  Class
• 5/3/04

2
Introduction

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

3
Mobile File Systems

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

4
Mobile vs. Stationary

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

5
Autonomy vs. Interdependence

• Balance between autonomy and interdependence
  necessary for optimal system performance
• Adaptability main goal of mobile file systems
  (compromise)

6
Mobile File Systems Characteristics

• Provide location transparency
• Provide replication (optimistic/pessimistic)
• Provide cache consistency
• Provide connected and disconnected operational
  modes
• Provide scalability

7
MFS Modes of Operation
8
Coda Distributed File System

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

9
Coda Client File Session
10
Coda Client States
11
Conclusions

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

12
References

• Satyanarayanan, M. Fundamental Challenges in
  Mobile Computing. Fifteenth ACM Symposium on
  Princ. of Distr. Comp. May 1996.
• Honeyman, P., Huston, L. B. Communications and
  Consistency in Mobile File Systems. IEEE
  Personal Communications, Dec. 1995, pp. 44-48.
• Braam, P. J. The Coda Distributed File System.
  Carnegie Mellon University. http//www.coda.cs.cm
  u.edu/ljpaper/lj.html.
• Schiller, J. Mobile Communications (2nd ed.).
  Addison-Wesley, 2003, pp. 375-381.
• Tanenbaum, A. S., van Steen, M. Distributed
  Systems Principles and Paradigms. Prentice
  Hall, 2002, pp. 604-623.