Cut-and-Paste file-systems: integrating simulators and file systems

We have implemented an integrated and configurable file system called the Pegasus filesystem (PFS) and a trace-driven file-system simulator called Patsy. Patsy is used for off-line analysis of file-systemalgorithms, PFS is used for on-line file-systemdata storage. Algorithms are first analyzed in Patsy and when we are satisfied with the performance results, migrated into PFS for on-line usage. Since Patsy and PFS are derived from a common cut-and-paste file-system framework, this migration proceeds smoothly. We have found this integration quite useful: algorithm bottlenecks have been found through Patsy that could have led to performance degradations in PFS. Off-line simulators are simpler to analyze compared to on-line file-systems because a work load can repeatedly be replayed on the same off-line simulator. This is almost impossible in on-line file-systems since it is hard to provide similar conditions for each experiment run. Since simulator and file-system are integrated (hence, use the same code), experiment results from the simulator have relevance in the real system. This paper describes the cut-and-paste framework, the instantiation of the framework to PFS and Patsy and finally, some of the experiments we conducted in Patsy.