Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Now showing 1 - 4 of 4
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    TACKLING PERFORMANCE AND SECURITY ISSUES FOR CLOUD STORAGE SYSTEMS
    (2022) Kang, Luyi; Jacob, Burce; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Building data-intensive applications and emerging computing paradigm (e.g., Machine Learning (ML), Artificial Intelligence (AI), Internet of Things (IoT) in cloud computing environments is becoming a norm, given the many advantages in scalability, reliability, security and performance. However, under rapid changes in applications, system middleware and underlying storage device, service providers are facing new challenges to deliver performance and security isolation in the context of shared resources among multiple tenants. The gap between the decades-old storage abstraction and modern storage device keeps widening, calling for software/hardware co-designs to approach more effective performance and security protocols. This dissertation rethinks the storage subsystem from device-level to system-level and proposes new designs at different levels to tackle performance and security issues for cloud storage systems. In the first part, we present an event-based SSD (Solid State Drive) simulator that models modern protocols, firmware and storage backend in detail. The proposed simulator can capture the nuances of SSD internal states under various I/O workloads, which help researchers understand the impact of various SSD designs and workload characteristics on end-to-end performance. In the second part, we study the security challenges of shared in-storage computing infrastructures. Many cloud providers offer isolation at multiple levels to secure data and instance, however, security measures in emerging in-storage computing infrastructures are not studied. We first investigate the attacks that could be conducted by offloaded in-storage programs in a multi-tenancy cloud environment. To defend against these attacks, we build a lightweight Trusted Execution Environment, IceClave to enable security isolation between in-storage programs and internal flash management functions. We show that while enforcing security isolation in the SSD controller with minimal hardware cost, IceClave still keeps the performance benefit of in-storage computing by delivering up to 2.4x better performance than the conventional host-based trusted computing approach. In the third part, we investigate the performance interference problem caused by other tenants' I/O flows. We demonstrate that I/O resource sharing can often lead to performance degradation and instability. The block device abstraction fails to expose SSD parallelism and pass application requirements. To this end, we propose a software/hardware co-design to enforce performance isolation by bridging the semantic gap. Our design can significantly improve QoS (Quality of Service) by reducing throughput penalties and tail latency spikes. Lastly, we explore more effective I/O control to address contention in the storage software stack. We illustrate that the state-of-the-art resource control mechanism, Linux cgroups is insufficient for controlling I/O resources. Inappropriate cgroup configurations may even hurt the performance of co-located workloads under memory intensive scenarios. We add kernel support for limiting page cache usage per cgroup and achieving I/O proportionality.
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    `Do-It-Yourself': Self-checkouts, Supermarkets, and the Self-Service Trend in American Business
    (2009) Andrews, Christopher K.; Landry, Bart; Sociology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A significant portion of sociology has always taken as its central focus the underlying relationship between economy and society. This dissertation continues this tradition by examining how self-service and its `do-it-yourself' ethos is changing the U.S. economy and the way in which Americans consume goods and services. Focusing upon the supermarket industry and the three principle stakeholder groups involved - employers, employees, and consumers - this dissertation examines why businesses are adopting automated checkout lanes. Particular attention is given to the reasons cited for their introduction, their effect upon work and employment in the industry, and the public's perception and attitude towards the technology. This dissertation adopts a multi-method approach, using information collected from eighty face-to-face interviews with customers, employees, and store managers, as well as secondary data and nonparticipant observation. Secondary data sources include published economic indicators and employment statistics, as well as information provided by newspapers and retail industry publications; nonparticipant observation was used to collect field notes documenting staffing levels, customer behavior, and other related information. Precisely why self-checkouts are being introduced remains a much-debated issue. Interviews indicate that organized labor and consumers view them as primarily a cost-cutting mechanism, yet labor costs within the industry continue to rise and employment remains relatively stable. At present, a number of social and economic barriers currently limit the extent of their use in stores; these factors include theft, maintenance, perceptions of service, internal controls, and specific labor contract provisions. Results also suggest that external, rather than internal, market factors may be driving current employment trends, including competition in the low-wage labor market and the emergence of non-union competition into the retail food industry. The benefits offered to consumers remains unclear. A majority of customers surveyed still prefer conventional cashier lanes, yet self-checkout clearly appeals to some consumers due to the perceived speed, control, and independence. However, results indicate that under most circumstances self-checkouts are not faster than conventional methods of checkout due to differences in user skill and experience. This may change, however, as similar self-service technologies become increasingly common in the service industry.
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    The Contributions of Demographic Background and Service-Learning Experiences to Undergraduates' Perceptions of Appreciation of Diversity
    (2005-05-25) Tongsri, Chirapar; Inkelas, Karen K.; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study investigated how race, gender, academic class standing, service involvement prior to college, and type of service-learning program may relate to students' perception of the contribution of service-learning on appreciation of diversity. The data were collected from 290 students at the University of Maryland, College Park in spring 2004, from a locally-created instrument. The findings revealed that there were significant differences in the reported contribution of service-learning to diversity appreciation between women and men and between freshmen and seniors, although there was no difference between races. Stepwise multiple regression indicated that aspects of class standing, type of service-learning program, race, and gender significantly predicted and contributed to the variance (8%) in students' reported contribution of service-learning to diversity appreciation. Further research should be conducted to better understand the role of race in this outcome as well as how practitioners can structure the service experience to enhance this outcome.
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    Service-learning and diversity: The relationship of race, gender, and prior service experience to students' self-perceived appreciation of difference and awareness of structural inequality
    (2004-08-10) Wilmarth, Laura Renee; McEwen, Marylu K; Counseling and Personnel Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis explored the relationship between students' participation in a one-semester service-learning course and their self-perceptions of diversity, defined as appreciation of difference and awareness of structural inequality (O'Grady, 2000). Specifically, the study explicated the relationship between each of the two diversity components and race, gender, service hours required, and prior service participation. The study utilized existing data from the Curricular Service Learning Survey, a locally developed instrument. Results indicated that women's perceptions of appreciation of difference were significantly greater than men's perceptions, whereas students' perceptions of awareness of structural inequality differed significantly by race and gender. Blocked hierarchical regressions revealed that students' prior service experience and high school service requirement predicted a significant but small amount of the variance (6%) in their perceptions of their appreciation of difference and that prior service experience predicted a significant amount of the variance (6%) in their awareness of structural inequality.