一个具有高可用性的动态容错VoD系统

提出了一个在VoD系统中具有高可用性的动态容错算法。针对分布式应用的特点,能对控制节点实现服务器切换的容错,数据服务节点负载均衡分配和故障节点提供服务的恢复。同时按照文章一致性保证机制可以实现媒体服务故障恢复对客户端的透明。通过对系统可用性分析和仿真试验表明,该算法可以有救地提高系统的可用性。     

分布式多服务器结构VoD系统的容错技术研究

分布式多服务器结构的VoD系统采用分布式存储技术将视频文件分块存储于不同的服务器上,如果没有良好的容错措施,某一服务器的故障将会导致整个系统无法运行。文章从算法角度分析了奇偶校验纠错法和线性编码法两种技术,分别适用于分布式多服务器结构的VoD系统在一个和多个服务器节点崩溃时恢复数据。     

改进LSTM-RF算法的传感器故障诊断与数据重构研究

针对传感器的故障诊断与故障数据重构问题,提出一种基于改进型长短期记忆网络(LSTM)和随机森林(RF)的混合算法.首先,运用改进型LSTM算法对传感器的输出序列进行预测,将预测值与实际值作差得到残差序列.然后,通过RF算法对残差序列进行分类,识别出传感器的故障状态.当传感器诊断的结果为故障工作状态时,利用改进型LSTM的预测值重构故障数据.所提的改进LSTM-RF算法在功能上既可以对传感器故障类型进行诊断,又可以对故障数据进行重构.实验结果表明,改进的LSTM-RF算法的传感器故障识别准确率在不同的数据集上均能大于97％,故障数据重构的均方根误差小于4％;相比标准的LSTM-RF算法,改进的LSTM-RF算法在收敛速度提高的同时故障数据重构的精度提高了0.4％.     

RAID控制器中矩阵重构方法研究

对于数据重构,纠删码提供了一个特定的编码方法,用于保护那些在磁盘阵列中的多重失效.在RAID的应用中,用纠删码为条块数据丢失建模,以便优化重构算法来重构整个条块.换句话说,它们只应用于高度相关的扇区故障,也就是在丢失磁盘上连续的扇区.定位了两个更一般的问题:①由分散或不相关的擦除导致丢失的数据的恢复;②由单个磁盘(存在许多故障时)导致的部分但连续的丢失数据的恢复.对两个问题所建议的方法是完全一般化的,并且能够应用于任何纠删码,但是此方法最适合基于异或的编码.对于分散的擦除,典型的是为每一个丢失扇区的数据规定了两种结果:要么这个丢失的数据被宣布为不可恢复,要么宣布为可恢复.并且,为只依赖于可读扇区的重构提供一个规则.简而言之,这个方法既完整又具有建设性.     

基于LMS算法的自适应逆可重构控制系统

针对多输入多输出(MIMO)飞控系统的可重构设计问题,提出了解耦控制与自适应逆控制(adaptive inverse control)相结合的控制策略.首先采用降阶线性动态逆(RLDI)设计了某型飞机的滚转角控制回路,以使飞机侧向运动的滚转与侧滑之间实现解耦;然后,考虑到当舵机出现故障以后系统性能的恢复问题,应用基于ε-滤波的LMS(least mean square)算法,在系统解耦的基础上构建了自适应逆控制系统,从而实现系统在舵机故障下的重构.仿真结果表明,这种基于改进的ε-滤波的LMS算法的自适应逆可重构飞行控制系统具有良好的系统故障恢复功能,表明了其在飞控系统中实施重构控制的有效性.     

直连网络中的动态自适应容错路由算法

针对超级计算机的直连网络发生链路或节点故障,需要在保证一定网络性能的前提下在线完成网络重构的问题,提出一种直连网络中的动态自适应容错路由算法.该算法能够承受空间和时间上任何数目故障的组合,使发生故障的系统经过自动重构后能够维持较优的计算能力.该算法不牺牲任何健康节点,并且无需过多硬件资源.模拟结果表明,在网络无故障的情况下几乎不影响直连网络的性能,数据结果也表明了故障恢复的实时性和有效性.     

负载自适应的存储池数据重构策略

大数据时代各应用领域对计算机存储系统的性能和可靠性需求与日俱增.新型存储介质为计算机存储系统的性能提升提供了良好的机遇,基于固态盘的存储阵列(RAIS)已在各种存储系统中广泛使用.传统RA IS系统中当一块固态盘出现故障时,通过数据重构操作恢复故障盘的数据,重构时间长,且影响对上层应用提供I/O访问服务的能力.针对该问...     

大规模层次化视频点播存储系统的设计与管理

近来计算机和通信技术的发展使得视频点播（video-on-demand,简称VOD)在技术和经济上成为可能.连续媒体的特性使得VOD系统需要大规模的存储服务器.层次化存储体系是减少系统费用的合理方案.文章提出了一种层次化的存储模型和磁盘cache的概念.根据这个模型,提出了基于访问频率的替换算法,并对算法的有效性进行了模拟和分析.结果表明,这种算法解决了LFU(least frequently used)算法中的“cache污染”（cache pollution）问题,能较好地适用于连续媒体数据应用.     

基于输出反馈特征结构配置的重构控制系统设计

推出了一种利用特征结构配置设计重构控制系统的新方法. 当故障后的系统满足m+r-1≥n的条件时, 通过重新设计一输出反馈增益阵, 使重构后的闭环故障系统的特征值全部恢复到故障前的位置, 特征向量也在可配置子空间中尽量接近故障前相应的闭环系统特征向量, 从而使重构后的系统性能最大程度地恢复到故障前的系统性能. 这种方法的优点是重构系统的稳定性可得到保证, 且计算输出反馈增益阵的算法相对简单. 应用实例和仿真结果说明本文方法的有效性.     

应用NctWare TTS避免FoxPro关联库的不彻底数据更新

一、NetWare TTS简介 TTS为事务跟踪系统(Transaction TrackingSystem)的简称。TTS是NetWare为保护工作站或服务器出现突然故障(死机或断电等)时数据库文件免遭破坏的一种方法。其工作原理是:在服务器SYS卷上开辟一定(一般小于400KB)的内存空间,在修改记录前将记录写入备份空间,出现故障时,TTS通过复制来恢复原先的内容。其工作流程是:     

A Design Framework for Multi-Resolution Video Servers

Video can be encoded into multiple-resolution format in nature. A multi-resolution or scalable video stream is a video sequence encoded such that subsets of the full resolution video bit stream can be decoded to recreate lower resolution video streams. Employing scalable video enables a video server to provide multiple resolution services for a variety of clients with different decoding capabilities and network bandwidths connected to the server. The inherent advantages of the multi-resolution video server include: heterogeneous client support, storage efficiency, adaptable service, and interactive operations support.For designing a video server, several issues should be dealt with under a unified framework including data placement/retrieval, buffer management, and admission control schemes for deterministic service guarantee. In this paper, we present a general framework for designing a large-scale multi-resolution video server. First, we propose a general multi-resolution video stream model which can be implemented by various scalable compression techniques. Second, given the proposed stream model, we devise a hybrid data placement scheme to store scalable video data across disks in the server. The scheme exploits both concurrency and parallelism offered by striping data across the disks and achieves the disk load balancing during any resolution video service. Next, the retrieval of multi-resolution video is described. The deterministic access property of the placement scheme permits the retrieval scheduling to be performed on each disk independently and to support interactive operations (e.g. pause, resume, slow playback, fastforward and rewind) simply by reconstructing the input parameters to the scheduler. We also present an efficient admission control algorithm which precisely estimates the actual disk workload for the given resolution services and hence permits the buffer requirement to be much smaller. The proposed schemes are verified through detailed simulation and implementation.     

Constructing a video server with tertiary storage: Practice and experience

Handling a tertiary storage device, such as an optical disk library, in the framework of a disk-based stream service model, requires a sophisticated streaming model for the server, and it should consider the device-specific performance characteristics of tertiary storage. This paper discusses the design and implementation of a video server which uses tertiary storage as a source of media archiving. We have carefully designed the streaming mechanism for a server whose key functionalities include stream scheduling, disk caching and admission control. The stream scheduling model incorporates the tertiary media staging into a disk-based scheduling process, and also enhances the utilization of tertiary device bandwidth. The disk caching mechanism manages the limited capacity of the hard disk efficiently to guarantee the availability of media segments on the hard disk. The admission controller provides an adequate mechanism which decides upon the admission of a new request based on the current resource availability of the server. The proposed system has been implemented on a general-purpose operating system and it is fully operational. The design principles of the server are validated with real experiments, and the performance characteristics are analyzed. The results guide us on how servers with tertiary storage should be deployed effectively in a real environment. RID="*" ID="*" e-mail: hjcha@cs.yonsei.ac.kr     

A Statistical Admission Control Scheme for Continuous Media Servers Using Caching

In continuous media servers, disk load can be reduced by using buffer cache. In order to utilize the saved disk bandwidth by caching, a continuous media server must employ an admission control scheme to decide whether a new client can be admitted for service without violating the requirements of clients already being serviced. A scheme providing deterministic QoS guarantees in servers using caching has already been proposed. Since, however, deterministic admission control is based on the worst case assumption, it causes the wastage of the system resources. If we can exactly predict the future available disk bandwidth, both high disk utilization and hiccup-free service are achievable. However, as the caching effect is not analytically determined, it is difficult to predict the disk load without substantial computation overhead. In this paper, we propose a statistical admission control scheme for continuous media servers where caching is used to reduce disk load. This scheme improves disk utilization and allows more streams to be serviced while maintaining near-deterministic service. The scheme, called Shortsighted Prediction Admission Control (SPAC), combines exact prediction through on-line simulation and statistical estimation using a probabilistic model of future disk load in order to reduce computation overhead. It thereby exploits the variation in disk load induced by VBR-encoded objects and the decrease in client load by caching. Through trace-driven simulations, it is demonstrated that the scheme provides near-deterministic QoS and keeps disk utilization high.     

Failure recovery algorithms for multimedia servers

In this paper, we present two novel disk failure recovery methods that utilize the inherent characteristics of video streams for efficient recovery. Whereas the first method exploits the inherent redundancy in video streams (rather than error-correcting codes) to approximately reconstruct data stored on failed disks, the second method exploits the sequentiality of video playback to reduce the overhead of online failure recovery in conventional RAID arrays. For the former approach, we present loss-resilient versions of JPEG and MPEG compression algorithms. We present an inherently redundant array of disks (IRAD) architecture that combines these loss-resilient compression algorithms with techniques for efficient placement of video streams on disk arrays to ensure that on-the-fly recovery does not impose any additional load on the array. Together, they enhance the scalability of multimedia servers by (1) integrating the recovery process with the decompression of video streams, and thereby distributing the reconstruction process across the clients; and (2) supporting graceful degradation in the quality of recovered images with increase in the number of disk failures. We present analytical and experimental results to show that both schemes significantly reduce the failure recovery overhead in a multimedia server.     

Design and Implementation of the Stony Brook Video Server

The system architecture of the Stony Brook Video Server (SBVS), which guarantees end-to-end real-time video playback in a client-server setting, is presented. SBVS employs a real-time network access protocol, RETHER, to use existing Ethernet hardware as the underlying communications media. The video server tightly integrates the bandwidth guarantee mechanisms for network transport and disk I/O. SBVS's stream-by-stream disk scheduling scheme optimizes the effective disk bandwidth without incurring significant scheduling overhead. To demonstrate the feasibility of the proposed architecture, we have implemented a prototype called SBVS-1, which can support five concurrent MPEG-1 video streams on an Intel 486DX2/EISA PC. To our knowledge, this system is the first video server that provides an end-to-end performance guarantee from the server's disks to the each user's display over standard Ethernet. This paper describes the implementation details of integrating network and I/O bandwidth guarantee mechanisms, and the performance measurements that drive and/or validate our design decisions. © 1997 by John Wiley & Sons, Ltd.     

Disk placement for arbitrary-rate playback in an interactive video server

Multimedia data, especially continuous media including video and audio objects, represent a rich and natural stimulus for humans, but require large amount of storage capacity and real-time processing. In this paper, we describe how to organize video data efficiently on multiple disks in order to support arbitrary-rate playback requested by different users independently. Our approach is to segment and decluster video objects and to place the segments in multiple disks using a restricted round-robin scheme, called prime round-robin (PRR). Its placement scheme provides uniform load balance of disks for arbitrary retrieval rate as well as normal playback, since it eliminates hot spots. Moreover, it does not require any additional disk bandwidth to support VCR-like operations such as fast-forward and rewind. We have studied the various effects of placement and retrieval schemes in a storage server by simulation. The results show that PRR offers even disk accesses, and the failure in reading segment by deadline occurs only at the beginning of new operations. In addition, the number of users admitted is not decreased, regardless of arbitrary-rate playback requests.     

视频服务器存储子系统的I/O优化

视频服务器存储子系统的I／O性能决定了视频服务器的总体性能。本文提出的一种新的实时磁盘调度算法（LLF－Window)能有效地服务各种编码格式的视频流，并对传统的SCSI总线不均衡调度机制进行了改造，实验结果表明，新的磁盘调度算法和改造后的SCSI总线调度机制有效地改进了视频服务器存储子系统的I／O性能，保证了视频流的连续播放。     

无盘技术在军内机密级办公网中的应用

无盘网络技术是一种网络终端用户没有硬盘等存储设备,通过网络存储管理器、服务器、以太网络传输模拟硬盘读写的一种技术。文章通过对无盘技术的分析与对比,提出了适合军内信息化建设的应用方案,为军内涉密信息的传递、共享、处理、存储和应用提供安全保障,实现涉密信息集中存储、涉密文档精确管理,严格控制涉密信息的输入输出,实现军内机密级办公网网络系统的安全管控。     

Resource scheduling in a high-performance multimedia server

Supporting continuous media data-such as video and audio-imposes stringent demands on the retrieval performance of a multimedia server. In this paper, we propose and evaluate a set of data placement and retrieval algorithms to exploit the full capacity of the disks in a multimedia server. The data placement algorithm declusters every object over all of the disks in the server-using a time-based declustering unit-with the aim of balancing the disk load. As for runtime retrieval, the quintessence of the algorithm is to give each disk advance notification of the blocks that have to be fetched in the impending time periods, so that the disk can optimize its service schedule accordingly. Moreover, in processing a block request for a replicated object, the server will dynamically channel the retrieval operation to the most lightly loaded disk that holds a copy of the required block. We have implemented a multimedia server based on these algorithms. Performance tests reveal that the server achieves very high disk efficiency. Specifically, each disk is able to support up to 25 MPEG-1 streams. Moreover, experiments suggest that the aggregate retrieval capacity of the server scales almost linearly with the number of disks     

基于磁盘系统的多用户视频准入算法

分析了基于磁盘系统的视频服务器的准入策略,提出了基于磁盘系统的为保证视频服务器接纳更大数目用户的准入算法,即在每个服务周期中每个用户要求检索到的数据块的数目与其对应的回放速率成比例,视频服务器通过过量预约资源来允许更大数量的客户数。这种算法允许视频服务器接纳更大数目的用户,满足多用户媒体回放的稳态性和迁移态连续性的要求。