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Understanding user and system behavior is most vital for designing efficient systems. Most systems are designed with certain user workload in mind. However, such workloads evolve over time, or the underlying hardware assumptions change. Further, most modern systems are not built or deployed in isolation, they interact with other systems whose behavior might not be exactly understood. Thus in order to understand the performance of a system, it must be inspected closely while user workloads are running. Such close inspection must be done with minimum disturbance to the user workload. Thus tracing or collection of all the user and system generated events becomes an important approach in gaining comprehensive insight in user behavior. As part of this work, we have three major contributions. We designed and implemented an in-depth block level I/O tracer, which would collect block level information like sector number, size of the I/O, actual contents of the I/O, along with certain file system information like filename, and offset in the file, for every I/O request. Next, to minimize the impact of the tracing to the running workload, we introduce and implement a sampling mechanism which traces fewer I/O requests. We validate that this sampling preserves certain I/O access patterns. Finally, as one of the application of our tracer, we use it as a crucial component of a system designed to do VM placements according to user workload. / Master of Science

Individual differences among users of a hierarchical file system were investigated. The results of a first experiment indicated that psychometric tests of vocabulary and spatial visualization were the best predictors of task performance, accounting for 45% of the variance in the data. The spatial predictor was found to be the most influential. This was dramatically illustrated by the fact that, on the average, subjects with low spatial ability took twice as long to perform the task as those with high spatial ability. Surprisingly, experience alone did not predict task performance. A comparison of the frequency of command usage between subjects with high and low spatial abilities revealed that those with low spatial ability were getting lost in the hierarchical file structure. Based on the concept of visual momentum, two changes to the interface were proposed. The changes consisted of a partial map of the hierarchy and an analog indicator of current file position. A second experiment compared the performance of users with high and low spatial abilities on the old Verbal interface and the new Graphical interface. The Graphical interface resulted in changes in command usage that were consistent with the predictions of the visual momentum analysis. Although these changes in strategy resulted in a performance advantage for the Graphical interface, the relative performance difference between High and Low Spatial groups remained constant across interfaces. However, the new interface did result in a decrease in the within-group variability in performance. / Master of Science

With the advent of high throughput sequencing technologies over the past decade there has been a surge in the amount of genomic data that needs to be analyzed and interpreted. Despite the availability of software frameworks such as the Genome Analysis Toolkit, data interpretation and analysis still requires human intervention and refinement. Genome browsers enable developers and users of sequence analysis tools to visualize, compare, and better interpret genomic data such as gene expression and functional annotations. We developed a next generation cross platform web-based genome browser, NextBrowse, for visualizing General Feature Format and Binary Alignment Map files. NextBrowse uses advanced visualization techniques such as 3D feature selection and transparency based on mapping quality, and improved Graphical User Interface elements such as individual track searching and textual and graphical reference location. NextBrowse is the first genome browser to allow BAM files to be streamed and visualized, the first genome browser to employ security measures, and the first to use only client side rendering. NextBrowse takes advantage of the open-source community, allowing developers and users to extend the project to fit their needs. NextBrowse along with all documentation is available for use at http://www.nextbrowse.vbi.vt.edu. / Master of Science