Design and implementation of a resource -efficient storage server for VoD

Yung Ryn Choe, Purdue University

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.

Degree

Ph.D.

Advisors

Pai, Purdue University.

Subject Area

Electrical engineering|Computer science

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