The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform

Vijay S. Pai - One of the best experts on this subject based on the ideXlab platform.

  • Design and implementation of a resource-efficient storage server for vod
    2007
    Co-Authors: Vijay S. Pai, Y.r. Choe
    Abstract:

    First, this dissertation presents a mathematical model and a prototype of a resource-efficient storage server for high-bitrate Video-on-Demand (VoD) applications. The model is detailed enough to account for the rate-based nature of streaming video, the buffering time allowed by the application, and average-case Disk hardware characteristics while remaining simple enough to use for algorithm and system design. This dissertation then describes a prototype storage server designed to serve large video files at the specified bitrates and finds its performance to agree closely with the model. Second, this dissertation investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for VoD workloads. A Disk array can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and “fail-stutter” faults that arise when the performance of one or more devices drops below expectations. This dissertation focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and randomization without duplication. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes. Third, this dissertation presents and evaluates Toast, a scalable VoD streaming system which combines the popular BitTorrent peer-to-peer (P2P) file-transfer technology with a simple dedicated streaming server to decrease server load and increase client transfer speed. The results show that the default BitTorrent download strategy is not well-suited to the VoD environment. Instead, strategies should favor downloading pieces of content that will be needed earlier, decreasing the chances that the clients will be forced to get the data directly from the VoD server. Such strategies allow Toast to operate much more efficiently than simple unicast distribution, reducing data transfer demands by up to 70–90% if clients remain in the system as seeds after viewing their content. Toast thus extends the aggregate throughput capability of a VoD service, offloading work from the server onto the P2P network in a scalable and demand-driven fashion.

  • IPDPS - Achieving Reliable Parallel Performance in a VoD Storage Server Using Randomization and Replication
    2007 IEEE International Parallel and Distributed Processing Symposium, 2007
    Co-Authors: Y.r. Choe, Vijay S. Pai
    Abstract:

    This paper investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for video-on-demand (VoD) workloads. A Disk array can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and "fail-stutter" faults that arise when the performance of one or more devices drops below expectations due to manufacturing variations, hardware problems, or geometry-related variations. This paper focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and randomization without duplication. The various allocation schemes are implemented and tested using a prototype VoD server with 2 dual-core Opteron processors, 8 SATA Disks, and 4 gigabit Ethernet interfaces running the Linux 2.6 kernel. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes.

  • Achieving Reliable Parallel Performance in a VoD Storage Server Using Randomization and Replication
    2007
    Co-Authors: Y.r. Choe, Vijay S. Pai
    Abstract:

    This paper investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for video-on-demand (VoD) workloads. A Disk ar-ray can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and “fail-stutter ” faults that arise when the per-formance of one or more devices drops below expectations due to manufacturing variations, hardware problems, or geometry-related variations. This paper focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and random-ization without duplication. The various allocation schemes are implemented and tested using a prototype VoD server with 2 dual-core Opteron processors, 8 SATA Disks, and 4 Gigabit Ethernet interfaces running the Linux 2.6 ker-nel. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes.

Shenze Chen - One of the best experts on this subject based on the ideXlab platform.

  • Design, modeling, and evaluation of high-performance I/O subsystems
    1992
    Co-Authors: Shenze Chen
    Abstract:

    In today's computer systems, the Disk I/O subsystem is often identified as a major bottleneck to system performance. Removing this bottleneck has proven to be a challenging research problem. The research reported in this dissertation is motivated by the design and performance issues of Disk I/O subsystems for a variety of today's computing systems. The goal is to design and evaluate high performance I/O subsystems for computing systems which support various applications. Our contributions are three-fold: for different application areas, we (1) propose new architecture and scheduling policies for the Disk I/O subsystems; (2) develop analytic models and simulators for these Disk subsystems; and (3) study and compare the performance of these architectures and scheduling policies. First, we study a mirrored Disk which can be found in various fault tolerant systems, where each data item is duplicated. While the primary purpose of Disk Mirroring is to provide the fault tolerance, we are interested in how to achieve performance gain by taking advantage of the two data copies. In particular, we propose and examine several policies which differ according to the manner in which read requests are scheduled to one of the two copies. Analytic models are developed to model the behavior of these policies and the best policies are proposed. In addition, the modeling techniques developed in this study are of independent interest, which can be used or extended to other system studies. Second, we investigate existing and propose new Disk array architectures for high performance computing systems. Depending on the applications, we propose scheduling policies suitable for these architectures. In particular, we study three variations of RAID 1, mirrored declustering, chained declustering, and group-rotate declustering. We compare the performance of RAID 5 versus Parity Striping. Finally, we examine the performance/cost trade-off of RAID 1 and RAID 5. The performance studies of the various Disk array architectures coupled with the proposed scheduling policies are based on our analytic models and simulators. Third, we examine the Disk I/O subsystems for real-time systems, where each I/O is expected to complete before a deadline. The goal is to minimize the fraction of requests that miss their deadlines. In doing so, we first propose two new real-time Disk scheduling algorithms, and compare them with other known real-time or conventional algorithms in an integrated real-time transaction system model. We then extend this study to a mirrored Disk and Disk arrays by combining the real-time algorithms with the architectures and policies studied before. Last, we study Disk I/O in a non-removal real-time system environment.

  • Performance of a mirrored Disk in a real-time transaction system
    ACM SIGMETRICS Performance Evaluation Review, 1991
    Co-Authors: Shenze Chen, Don Towsley
    Abstract:

    Disk Mirroring has found widespread use in computer systems as a method for providing fault tolerance. In addition to increasing reliability, a mirrored Disk can also reduce I/O response time by supporting the execution of parallel I/O requests. The improvement in I/O efficiency is extremely important in a real-time system, where each computational entity carries a deadline. In this paper, we present two classes of real-time Disk scheduling policies, RT-DMQ and RT-CMQ, for a mirrored Disk I/O subsystem and examine their performance in an integrated real-time transaction system. The real-time transaction system model is validated on a real-time database testbed, called RT-CARAT. The performance results show that a mirrored Disk I/O subsystem can decrease the fraction of transactions that miss their deadlines over a single Disk system by 68%. Our results also reveal the importance of real-time scheduling policies, which can lead up to a 17% performance improvement over non-real-time policies in terms of minimizing the transaction loss ratio.

  • SIGMETRICS - Performance of a mirrored Disk in a real-time transaction system
    Proceedings of the 1991 ACM SIGMETRICS conference on Measurement and modeling of computer systems - SIGMETRICS '91, 1991
    Co-Authors: Shenze Chen, Don Towsley
    Abstract:

    Disk Mirroring has found widespread use in computer systems as a method for providing fault tolerance. In addition to increasing reliability, a mirrored Disk can also reduce I/O response time by supporting the execution of parallel I/O requests. The improvement in I/O efficiency is extremely important in a real-time system, where each computational entity carries a deadline. In this paper, we present two classes of real-time Disk scheduling policies, RT-DMQ and RT-CMQ, for a mirrored Disk I/O subsystem and examine their performance in an integrated real-time transaction system. The real-time transaction system model is validated on a real-time database testbed, called RT-CARAT. The performance results show that a mirrored Disk I/O subsystem can decrease the fraction of transactions that miss their deadlines over a single Disk system by 68%. Our results also reveal the importance of real-time scheduling policies, which can lead up to a 17% performance improvement over non-real-time policies in terms of minimizing the transaction loss ratio.

Don Towsley - One of the best experts on this subject based on the ideXlab platform.

  • Performance of a mirrored Disk in a real-time transaction system
    ACM SIGMETRICS Performance Evaluation Review, 1991
    Co-Authors: Shenze Chen, Don Towsley
    Abstract:

    Disk Mirroring has found widespread use in computer systems as a method for providing fault tolerance. In addition to increasing reliability, a mirrored Disk can also reduce I/O response time by supporting the execution of parallel I/O requests. The improvement in I/O efficiency is extremely important in a real-time system, where each computational entity carries a deadline. In this paper, we present two classes of real-time Disk scheduling policies, RT-DMQ and RT-CMQ, for a mirrored Disk I/O subsystem and examine their performance in an integrated real-time transaction system. The real-time transaction system model is validated on a real-time database testbed, called RT-CARAT. The performance results show that a mirrored Disk I/O subsystem can decrease the fraction of transactions that miss their deadlines over a single Disk system by 68%. Our results also reveal the importance of real-time scheduling policies, which can lead up to a 17% performance improvement over non-real-time policies in terms of minimizing the transaction loss ratio.

  • SIGMETRICS - Performance of a mirrored Disk in a real-time transaction system
    Proceedings of the 1991 ACM SIGMETRICS conference on Measurement and modeling of computer systems - SIGMETRICS '91, 1991
    Co-Authors: Shenze Chen, Don Towsley
    Abstract:

    Disk Mirroring has found widespread use in computer systems as a method for providing fault tolerance. In addition to increasing reliability, a mirrored Disk can also reduce I/O response time by supporting the execution of parallel I/O requests. The improvement in I/O efficiency is extremely important in a real-time system, where each computational entity carries a deadline. In this paper, we present two classes of real-time Disk scheduling policies, RT-DMQ and RT-CMQ, for a mirrored Disk I/O subsystem and examine their performance in an integrated real-time transaction system. The real-time transaction system model is validated on a real-time database testbed, called RT-CARAT. The performance results show that a mirrored Disk I/O subsystem can decrease the fraction of transactions that miss their deadlines over a single Disk system by 68%. Our results also reveal the importance of real-time scheduling policies, which can lead up to a 17% performance improvement over non-real-time policies in terms of minimizing the transaction loss ratio.

Y.r. Choe - One of the best experts on this subject based on the ideXlab platform.

  • Design and implementation of a resource-efficient storage server for vod
    2007
    Co-Authors: Vijay S. Pai, Y.r. Choe
    Abstract:

    First, this dissertation presents a mathematical model and a prototype of a resource-efficient storage server for high-bitrate Video-on-Demand (VoD) applications. The model is detailed enough to account for the rate-based nature of streaming video, the buffering time allowed by the application, and average-case Disk hardware characteristics while remaining simple enough to use for algorithm and system design. This dissertation then describes a prototype storage server designed to serve large video files at the specified bitrates and finds its performance to agree closely with the model. Second, this dissertation investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for VoD workloads. A Disk array can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and “fail-stutter” faults that arise when the performance of one or more devices drops below expectations. This dissertation focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and randomization without duplication. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes. Third, this dissertation presents and evaluates Toast, a scalable VoD streaming system which combines the popular BitTorrent peer-to-peer (P2P) file-transfer technology with a simple dedicated streaming server to decrease server load and increase client transfer speed. The results show that the default BitTorrent download strategy is not well-suited to the VoD environment. Instead, strategies should favor downloading pieces of content that will be needed earlier, decreasing the chances that the clients will be forced to get the data directly from the VoD server. Such strategies allow Toast to operate much more efficiently than simple unicast distribution, reducing data transfer demands by up to 70–90% if clients remain in the system as seeds after viewing their content. Toast thus extends the aggregate throughput capability of a VoD service, offloading work from the server onto the P2P network in a scalable and demand-driven fashion.

  • IPDPS - Achieving Reliable Parallel Performance in a VoD Storage Server Using Randomization and Replication
    2007 IEEE International Parallel and Distributed Processing Symposium, 2007
    Co-Authors: Y.r. Choe, Vijay S. Pai
    Abstract:

    This paper investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for video-on-demand (VoD) workloads. A Disk array can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and "fail-stutter" faults that arise when the performance of one or more devices drops below expectations due to manufacturing variations, hardware problems, or geometry-related variations. This paper focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and randomization without duplication. The various allocation schemes are implemented and tested using a prototype VoD server with 2 dual-core Opteron processors, 8 SATA Disks, and 4 gigabit Ethernet interfaces running the Linux 2.6 kernel. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes.

  • Achieving Reliable Parallel Performance in a VoD Storage Server Using Randomization and Replication
    2007
    Co-Authors: Y.r. Choe, Vijay S. Pai
    Abstract:

    This paper investigates randomization and replication as strategies to achieve reliable performance in Disk arrays targeted for video-on-demand (VoD) workloads. A Disk ar-ray can provide high aggregate throughput, but only if the server can effectively balance the load on the Disks. Such load balance is complicated by two key factors: workload hotspots caused by differences in popularity among media streams, and “fail-stutter ” faults that arise when the per-formance of one or more devices drops below expectations due to manufacturing variations, hardware problems, or geometry-related variations. This paper focuses on the random duplicate assignment (RDA) data allocation policy which places each data block on two Disks chosen at random, independent of other blocks in the same media stream or other streams. This strategy is compared to traditional single-Disk file allocation, Disk striping (RAID-0), Disk Mirroring (RAID-1), and random-ization without duplication. The various allocation schemes are implemented and tested using a prototype VoD server with 2 dual-core Opteron processors, 8 SATA Disks, and 4 Gigabit Ethernet interfaces running the Linux 2.6 ker-nel. The results indicate that combining randomization and replication allows RDA to effectively tolerate both workload hotspots and fail-stutter faults better than previous schemes.

Mohammad Reza Meybodi - One of the best experts on this subject based on the ideXlab platform.

  • RAID-RMS: A fault tolerant stripped Mirroring RAID architecture for distributed systems
    Computers & Security, 2008
    Co-Authors: Javad Akbari Torkestani, Mohammad Reza Meybodi
    Abstract:

    Disk arrays, or RAIDs, have become the solution to increase the capacity, bandwidth and reliability of most storage systems. In spite of its high redundancy level, Disk Mirroring is a popular RAID paradigm, because replicating data also doubles the bandwidth available for processing read requests, improves the reliability and achieves fault tolerance. In this paper, we present a new RAID architecture called RAID-RMS in which a special hybrid mechanism is used to map the data blocks to the cluster. The main idea behind the proposed algorithm is to combine the data block striping and Disk Mirroring technique with a data block rotation. The resulting architecture improves the parallelism reliability and efficiency of the RAID array. We show that the proposed architecture is able to serve many more Disk requests compared to the other Mirroring-based architectures. We also argue that a more balanced Disk load is attained by the given architecture, especially when there are some Disk failures.