The influence of scale on distributed file system design

The proposition that scale should be recognized as a primary factor influencing the architecture and implementation of distributed systems is validated using Andrew and Coda, two distributed file systems. Performance, operability, and security are dominant considerations in the design of these systems. Availability is a further consideration the design of Coda. Client caching, bulk data transfer, token-based mutual authentication and hierarchical organization of the protection domain have emerged as mechanisms that enhance scalability. The separation of concerns made possible by functional specialization has also proved valuable in scaling. Heterogeneity is an important by-product of growth, but the mechanisms available to cope with it are rudimentary. Physical separation of clients and servers turns out to be a critical requirement for scalability     

Mobile computing

The problems, limitations, and potential advantages of mobile computing systems are discussed. It is suggested that the constraints violate many of the assumptions upon which today's distributed systems are based. A key requirement of mobile computing systems will be the ability to access critical data regardless of location, which implies interdependence between the elements of a mobile computing system. The Coda file system, which is an effort to provide transparency of environment to mobile computing systems, is reviewed     

采用信任管理的分布式文件系统TrustFs

在传统的分布式文件系统中用户无法判断文件的可信任性,针对此问题提出采用信任管理的分布式文件系统TrustFs,使用数字签名对文件的发布者进行认证,通过信任管理技术评估发布者的可信任度,从而达到帮助用户识别不安全文件的目的。TrustFs使用可堆叠文件系统的技术实现,可以移植到所有的Unix系统,并具有良好的扩展性。     

COSMOS文件系统的性能分析

COSMOS文件系统提供单一系统映象和严格的UNIX语义,提供与UNIX文件系统的应用程序二进制兼容,系统中没有引入集中的服务器瓶颈,所有的数据、元数据和目录文件都被分散存储在整个系统中,以提供高性能和良好的可扩展性,测试表明,COSMOS文件系统具有很好的系统带宽和整体性能,系统具有良好的可扩展性,文中讨论了影响系统性能和可扩展性的关键因素,基于作者的实现经验和测试数据,讨论了现有系统中存在的性能瓶颈并且提出了改进的方案。     

An Installable Version Control File System for Unix

We present a file system named VCFS, a Version Control File System that provides transparent version control of files. VCFS is implemented as an installable file system in the Unix operating system. The facility is transparent to users in the sense that VCFS automatically stores changes between incremental versions of a file without user intervention. Access to the latest version of the file retains traditional Unix semantics, enabling all existing Unix applications to be run modified under VCFS if so desired. VCFS provides system call enhancements and supports application level utilities for version number retrieval, displaying changes between two versions of a file, upgrading to a new release number, and related version control functions. Performance measurements show that VCFS provides a significant increase in version control operations compared to application level change management systems such as SCCS, and that the space utilization is significantly better than of the existing version control systems. The primitives and facilities provided by VCFS can be exploited for use in a wide range of applications, ranging from immutable files, transaction processing and file replication support in a distributed file system, to the development of enhanced change management control systems for software project management. © 1997 John Wiley & Sons, Ltd.     

基于Web的跨平台分布式多线程文件服务器设计

分析了以往分布式文件服务器的不足,提出了一种以J2EE技术为核心的基于Web的跨平台分布多线程文件服务器的设计方案,该分布式文件服务器由一个集中控制单元和多个本地文件服务器组成,集中控制单元以数据库的地文件逻辑信息进行集中式管理,文件的物理信息则上位于Web不同节点上的本地文件服务器分布式地管理,本地文件服务器支持多线程文件操作和Windows,Unix,Linux等多种操作系统的文件系统。     

基于虚拟文件操作的文件检查点设置

实现分布/并行系统容错的基础是单进程检查点设置和卷回恢复技术,而对活动文件信息进行保存和恢复则是这种技术的重要方面.提出一种虚拟文件操作策略,实现了对用户文件的检查点设置,有效地解决了发生故障时用户文件内容与进程全局状态的不一致的问题.该方法通过文件块式管理、检查点分布操作等技术,使得在空间开销、正常运行时间、恢复时间等性能指标上优于其他方法,并且具有对用户透明、可最大限度地保留已完成工作的特点.     

QoS-based evaluation of file systems and distributed system services for continuous media provisioning

This paper presents a QoS-based performance analysis of file systems and distributed object services for Continuous Media (CM) provisioning, as well as the details and implementation experiences of a continuous media file system and associated CM servers. For this we have implemented QoS-driven CM servers and the Presto continuous media file system (PFS) in the context of a distributed multimedia application development environment, and validate the performance of PFS against that of the conventional Unix file system through an experimental evaluation. Using our CM server prototype, we next examine the effect of continuous media data delivery on the three different kinds of network protocols such as CORBA, UDP/IP, and TCP/IP, with respect to QoS provisioning and throughput.     

Efficient data distribution in a Web server farm

High-performance Web sites rely on Web server `farms', hundreds of computers serving the same content, for scalability, reliability, and low-latency access to Internet content. Deploying these scalable farms typically requires the power of distributed or clustered file systems. Building Web server farms on file systems complements hierarchical proxy caching. Proxy caching replicates Web content throughout the Internet, thereby reducing latency from network delays and off-loading traffic from the primary servers. Web server farms scale resources at a single site, reducing latency from queuing delays. Both technologies are essential when building a high-performance infrastructure for content delivery. The authors present a cache consistency model and locking protocol customized for file systems that are used as scalable infrastructure for Web server farms. The protocol takes advantage of the Web's relaxed consistency semantics to reduce latencies and network overhead. Our hybrid approach preserves strong consistency for concurrent write sharing with time-based consistency and push caching for readers (Web servers). Using simulation, we compare our approach to the Andrew file system and the sequential consistency file system protocols we propose to replace     

A Unix-to-Versados link

In this paper the implementation of CV, a utility for calling up the Versados system under Unix, is described. CV provides useful resource-sharing features to Unix users such as file transfers between the two systems and accessibility of a real-time environment. The implementation of the Unix-to-Versados link requires detailed knowledge of the hardware and software interfaces of the systems. Problems encountered and their solutions are discussed; the experience gained here could be useful to others in solving similar problems.     

A Distributed Real-Time Operating System

A distributed real-time operating system, Fados, has been developed for an embedded multiprocessor system. The operating system is based on a host-target approach and provides for communication between arbitrary processes on host and target machines. The facilities offered are, apart from process communication, access to the file system on the host by programs on the target machine and monitoring and debugging of programs on the target machine from the host. The process communication has been designed in such a way that the possibilities are the same as those offered by the Ada programming language. The operating system is implemented on an MC 68000 based multiprocessor system in combination with a Unix

1 Unix is a trademark of A. T. & T. Bell laboratories.

host.     

Unix进程检查点设置关键技术

Unix进程的检查点设置是实现分布/并行系统容错、重播调试、进程迁移、系统模拟和作业切换等功能的基础。该论文主要论述UNIX进程检查点基本信息的保存与恢复、文件检查点、检查点信息的优化等关键技术,最后介绍Libckpt、Condor以及自行设计的Libcsm等检查点设置工具。     

分布式文件系统低耦合度高可用性支持模块的实现

与现有的分布式文件系统的惯例——把数据高可用性的实现融合在文件系统中——不同，设计了一个数据高可用性子系统(data high availability module，DHAM)，用于为分布式文件系统提供数据高可用性支持．设计子系统的基本指导思想是把文件系统的高可用性实现从文件系统中抽取出来，作为一个单独的模块来实现，弱化它与文件系统其他部分之间的耦合性，使得二者之间仅仅有简单的接口关系．目的是使文件系统的设计更加模块化，并且便于对文件系统的容错这一主题进行专门的研究．DHAM已经成功地用于本研究所白行开发的分布式文件系统Clufs中，为其提供了数据高可用性支持．最后给出了模块的功能及性能测试结果，并对采用此模块前、后系统的出错概率进行了理论分析.     

Accessing files in an Internet: the Jade file system

The Jade file system, which provides a uniform way to name and access files in an Internet environment, is introduced. Jade is a logical system that integrates a heterogeneous collection of existing file systems in which underlying file systems support different file access protocols. Because of autonomy, Jade is designed under the restriction that the underlying file systems may not be modified. In order to avoid the complexity of maintaining an Internet-wide, global name space, Jade permits each user to define a private name space. Jade's name space supports two features: it allows multiple file systems to be mounted under one directory, and it permits one logical name space to mount other logical name spaces. A prototype of Jade has been implemented to examine and validate its design. The prototype consists of interfaces to the Unix File System, the Sun Network File System, and the File Transfer Protocol. An overview of Jade's design is reported, and the authors' experiences in designing and implementing a large scale file system are reviewed     

Unix文件系统安全管理的研究

文章根据Unix文件系统的特点,从系统安全管理方面着手,对Unix系统的用户帐号、用户口令、系统存储设备管理和检测等方面进行了多层次的讨论与分析,并采取行之有效的安全防范措施,从而提高Unix系统的安全性和可靠性.     

FlexiFrag: A design pattern for flexible file sharing in distributed collaborative applications

The need for flexible file sharing in distributed systems is increasing in applications such as calendar management, collaborative editing of documents, collaborative software developments etc. The file sharing policies required in these applications are often very different from the traditional read/write policies. Hence, a flexible way of specifying and implementing sharing policies on individual files in file systems is required. We propose a distributed object-based system model of constructing file systems. The object-based system model is based on a pattern called FlexiFrag. We show how a distributed object-based system and in particular distributed file system can be constructed using the pattern in a flexible way.     

基于Web的无组件资源管理系统的设计与实现

随着计算机技术和网络应用的发展,人们利用网络来管理个人文件的需求越来越大。本文简单介绍了目前常见的网络文件管理系统的设计特点,并详细提出了一个利用J2EE规范设计实现无组件资源管理系统的方案。该方案实现的系统具有强大的检索和文件分类功能,实现了基于Web的无组件多文件／文件夹上传,并且可灵活地调度和管理文件。
与现有的其他网络文件管理系统相比,该系统有较明显的优点。在实际应用中,该系统也取得了较好的效果。     

Project Athena as a distributed computer system

Project Athena, established in 1983 to improve the quality of education at MIT (Massachussetts Institute of Technology) by providing campuswide, high-quality computing based on a large network of workstations, is discussed, focusing on the design of Athena's distributed workstation system. The requirements of the system are outlined distributed system models are reviewed, other distributed operating systems are described, and issues in distributed systems are examined. The distributed-system model for Athena is discussed. Athena has three major components; workstations a network, and servers. The approach taken by the Athena developers was to implement a set of network services to replace equivalent time-sharing services, in essence converting the time-sharing Unix model into a distributed operating system     

Measuring software dependability by robustness benchmarking

Inability to identify weaknesses or to quantify advancements in software system robustness frequently hinders the development of robust software systems. Efforts have been made to develop benchmarks of software robustness to address this problem, but they all suffer from significant shortcomings. The paper presents the various features that are desirable in a benchmark of system robustness, and evaluates some existing benchmarks according to these features. A new hierarchically structured approach to building robustness benchmarks, which overcomes many deficiencies of past efforts, is also presented. This approach has been applied to building a hierarchically structured benchmark that tests part of the Unix file and virtual memory systems. The resultant benchmark has successfully been used to identify new response class structures that were not detected in a similar situation by other less organized techniques