File Access Patterns in Coda Distributed File System

Distributed File Systems have long utilized file caching techniques to improve performance. In many DFS’s clients are allowed to update the cached replicas of files, necessitating a variety of mechanisms that ensure the consistency of other replicas of these files across the network. This problem becomes complicated if there are many unstable files on the network, and especially so if there are no central servers. Surprisingly, there has not been much research into the access patterns of shared files. While researchers have found that there are relatively few unstable files, this claim has been disputed by others, and the last such study that I am aware of dates back to 1992. Even more strikingly, I am aware of no detailed studies of file reading and writing patterns at all. In an attempt to fill this gap, I analyzed file access patterns in Coda Distributed File System using traces collected at Carnegie Mellon University over a period of approximately two years. I found that 1) Most files analyzed are stable; 2) Most unstable files tend to be updated and read by only one computer, but the computer that reads a file tends to be different from the one that updates it; and 3) A vast majority of files are read by the same computer that created them.