Exploiting Weak Connectivity for Mobile File Access

Lily B. Mummert, Maria R. Ebling, M. Satyanarayanan


Weak connectivity, in the form of intermittent, low-bandwidth, or expensive networks is a fact of life in mobile computing. In this paper, we describe how the Coda File System has been evolved to exploit such networks. The underlying theme of this evolution has been the identification of hidden assumptions about strong connectivity, and their systematic elimination through the introduction of adaptivity. Many aspects of the system, including communication, cache validation, update propagation and cache miss handling have been affected. As a result, Coda is able to provide good performance to users even when network bandwidth varies over four orders of magnitude --- from modem speeds to LAN speeds. Users are affected by network quality mainly in the promptness with which updates are propagated, and in the degree of transparency with which cache misses are handled.