隨選視訊應用中降低儲存系統資源需祈求的方法

Abstract

多媒體系統由於結合了多種不同的資料形態, 包括:文字,圖形,影像,動 畫,聲音,視訊影片等,已廣泛地運用在各種不同的應用系統當中. 目前對 於多媒應用方面的研究主要分為兩大類,一類是在獨立的電腦主機上之應 用,如電腦輔助教學,電腦作曲,影片播放. 另一類是透過網路在分散式環 境上之應用,如遠距教學,視訊會議,隨選視訊服務. 我們的研究主要著重 在隨選視訊服務上的應用. 隨選視訓系統和傳統純文字系統最大的差別在 於聲音和視訊資料的特性. 首先,聲音和視訊資料因為有連續性,系統必須 在要求的時間內取得所需的資料,才能維持連續播放的品質. 再者,即使是 經過壓縮,聲音和視訊資料對於系統資源的需求仍相當大,特別是在儲存空 間和資料存取頻寬上的需求. 由於這兩方面的特性,欲提供隨選視訊的服 務勢必需要一個能提供大量儲存空間,與高資料傳輸速率的儲存系統.就目 前在儲存系統上所發展的技術而言,欲同時提供多人隨選視訊的服務仍存 在相當的技術瓶頸有待克服. 因此,在提供這類服務時,如何減少對儲存系 統所需的資源,便成了克服此瓶頸的重要方法之一. 而我們的研究便是提 出並分析比較一些在隨選視訊應用中減少對儲存系統資源需求的方法,以 提高系統能同時服務的使用者人數. 我們不只考慮系統在正常運作時的狀 態, 也考慮了當系統因磁碟損壞而處於不正常運作的狀態.我們利用了一 些在緩衝區管理方面的技術,來減少系統在正常運作狀態下對儲存系統的 資源需求,同時提出了一個新的磁碟陣列架構,來減少系統在不正常運作狀 態下對儲存系統的資源需求. 根據分析及模擬實驗證明我們所提的方法, 確實能解決隨選視訊應用在儲存系統上所面臨的瓶頸. hics, animation, images, audio, and full-motion video, into a wide rangeof applications. Research and development efforts in multimedia computingfall into two groups. One group centers its efforts on the stand-alone multimedia workstation and associated software systems, such as musiccomposition, computer-aided learning, and interactive video. The other group combines multimedia computing with distributed systems, such as distance learning, on-demand multimedia services, and video-based conferencing systems. Multimedia data differ substantially from those of conventional applications with regard to three aspects. First, audio and video data are delay-sensitive. A multimedia system must ensure that continuity and real-time requirements are not violated. Second, a multimediaobject may consist of multiple components: audio, video, text, ..., etc. It isthe responsibility of the system to ensure that these multiple streams can be synchronized during retrieval. Third, audio and video data (even compressed)consume large amounts of system resources - primarily storage space and bandwidth.The characteristics of multimedia applications stresses all the components of acomputer system, especially, the storage systems which require very high capacity,fast access time, and high transfer rate.Due to limitations of current storage technology, reducing I/O demands in storagesubsystems becomes an important issue for video servers to provide more services. In this dissertation, we design and analyze the techniques of reducing I/O demandsfor video-on-demand storage servers. Both normal and failure states of the storageserver are considered. Normal state is during the period when all disks in thestorage server are operational and failure state is during the period when diskkfailures occur. The failure-state performance is significant for video-on-demandapplications in which continuous operation is of concern. We develop some buffermanagement techniques to reduce I/O demands in normal state, and design a newvariation of disk arrays to reduce I/O operations in the presence of disk failures.The experimental results reveal that our proposed buffer management mechanismsenable a video server to support more users simultaneously in normal state and thatour disk array architecture reduces the performance degradation of a video serverin failure state.