| I/O has become the major bottleneck in application performance, as processor speed has skyrocketed over the last few years, leaving storage hardware and file systems struggling to be competitive. This research presented a new methodology to evaluate workload-dependent file system performance. Applying the new methodology, the conducted benchmarks served as a baseline for the design of a new file data allocation algorithm for extent based file systems.; The constructed performance hierarchy incorporates performance dependencies at all levels of a system, which allows comparing, evaluating, and analyzing vectors, a single, application specific metric allows the analyst to conduct a sensitivity study. The characterization vectors and the resulting single metric satisfy all the potential demands for analyzing I/O performance, in particular systems evaluation, comparison, and optimization. The main argument made throughout this study is that systems performance has to be measured in the context of a particular application and a particular workload. The performance evaluation methodology presented in this thesis enables such measurements. The file system benchmarks conducted on VxFS and UFS file systems respectively disclosed the strengths and weaknesses of an extent-based and a block-based file system design. In both architectures, fragmentation substantially impacts I/O performance as the file systems age. The performance measurements outlined the correlation between internal and external fragmentation, and made a strong case for a much enhanced file data allocation algorithm for extent based file systems. The second part of this research introduced a new file data allocation algorithm for extent based file systems. The introduced allocation algorithm fulfilled the major requirements of increasing I/O performance by lowering fragmentation without significantly increasing the metadata overhead. The presented analytical data model, as well as the actual simulation of the new file data allocation algorithm, proofed the great potential of the new design. |
