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Browsing by Author "Won, Youjip"

Now showing 1 - 3 of 3
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    Coping with Excessive Memory Requirement Under I/O Bandwidth Congestion
    (1997) Won, Youjip; Srivastava, Jaideep
    In this paper, we investigate the buffer requirement in retrieving the continuous media streams from the disk subsystem. Memory buffer is used to synchronize asynchronous disk read operation and synchronous playback operation. In supporting a set of continuous media playbacks, as aggregate bandwidth required increases, larger amount of buffer needs to ibe allocated. This characteristics originates from the increase in cycle length. It is well known fact that as disk utilization approaches I 00%, total buffer to support the playbacks increases extremely fast. Conservative estimation on disk usage is thus advised in designing disk subsystem for continuous media server. However, in the practical situation aggregate bandwidth may increase over the expected value, and may consume excessive amount of buffer memory. The focus of this is to an algorithm coping with this excessive buffer requirement under bandwidth congestion. We argue that in a large scale continuous media server, where user access pattern is biased and there are frequent request arrivals, it is not necessary to maintain the playback directly from the disk for each request in supporting a set of timely interleaved playbacks. We define two mechanisms to service a playback request, namely disk mode and memory mode. In memory mode, request is supplied data blocks which was loaded by preceding request. We develop an efficient algorithm to determine the optimal service mode for a set of playback request minimizing overall buffer requirement.
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    Issues in Designing a Distributed Hierarchical Storage System for Continuous Media Service
    (1997) Won, Youjip
    Recent advances in computing and communication technologies have made it technically feasible and economically viable to provide on-line access to a variety of information services over high speed networks. Particularly, convergence of various technological factors, namely in network access and in video coding and transmission, have recently brought a rapid growth of interest in on-line access to multimedia services. Large-scale provision of such service is attractive end users as well as service providers. However, excessive bandwidth and space requirements of continuous media data have been a serious impediment to the wide spread usage of on-line continuous media services, especially in the commercial entertainment market. In this dissertation, we propose distributed hierarchical storage architecture as a promising solution to cost-effective service provisioning. The advantage of adopting a hierarchical storage architecture is its ability to assign the appropriate storage hierarchy to each file based on its the access frequency. However, success in using a storage hierarchy relies upon selecting appropriate operational parameters with a given user access profile. Our hierarchical storage system consists of primary storage, secondary storage, and tertiary storage. This dissertation analyzes the performance of the hierarchical storage system under various combinations of system attributes and develops a technique to find the minimum amount of resources in each level of hierarchies while satisfyin'g certain operational constraints. The second part of the dissertation, the effort focuses on distributed service provisioning. Techniques are developed to exploit the geographical locality of reference and temporal locality of reference by introducing intermediate storages. Due to non-trivial network resource requirement, it is beneficial to put the data closer to the end user. To precisely compute the trade-offs between network resource consumption and storage resource cost, we develop a cost model which quantifies the aggregate resource consumption. On the basis of the cost model, an algorithm which finds the efficient way of servicing a set of requests is developed. The observations and finding from the mathematical models are validated with the simulation studies.
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    Parametric Evaluation of Performance Behavior in Hierarchical Storage Architecture
    (1997) Won, Youjip; Srivastava, Jaideep
    In this article, we investigate lhe performance behavior of a hierarchical storage architecture. Considering both the size of video files and the skewed file access patterns over the available files, it is not cost-effective to store all video files on secondary storage such as disk arrays, since most users may access only a small subset of the available video files. Using tertiary storage, such as a tape library, is a promising solution for achieving the desired cost effectiveness. Though a hierarchical storage structure is desirable, an unbalanced configuration of the storage hierarchy may result in waste of resources and thus degrade overall server throughput. Our effort is focused on investigating the effect of the various system parameters to obtain an optimal configuration of the hierarchical storage. Throughput of the server is defined along with two orthogonal performance metrics, namely expected service rime and system congestion and blocking probability. We establish an analytical formulation for the given performance metrics. Hierarchical storage performance is governed by several factors such as user-access pattern, number of tape drives, capacity of secondary storage, transfer rate of tape drives, and transfer rate of disks. It is observed that speeding up the rate of data transfer may in some cases increase the blocking probability and hence degrade overall server performance. We use a queuing model to obtain an analytical formulation of the server's performance. This enables us to investigate the effects of different configurations of the storage hierarchy and different data access patterns; it also provides a framework to determine the optimal configuration of storage hierarchies. The results of a simulation-based performance evaluation are also presented.