Deceit: A flexible distributed file system

Deceit, a distributed file system (DFS) being developed at Cornell, focuses on flexible file semantics in relation to efficiency, scalability, and reliability. Deceit servers are interchangeable and collectively provide the illusion of a single, large server machine to any clients of the Deceit service. Non-volatile replicas of each file are stored on a subset of the file servers. The user is able to set parameters on a file to achieve different levels of availability, performance, and one-copy serializability. Deceit also supports a file version control mechanism. In contrast with many recent DFS efforts, Deceit can behave like a plain Sun Network File System (NFS) server and can be used by any NFS client without modifying any client software. The current Deceit prototype uses the ISIS Distributed Programming Environment for all communication and process group management, an approach that reduces system complexity and increases system robustness

A distributed file service based on optimistic concurrency control

The design of a layered file service for the Amoeba Distributed System is discussed, on top of which various applications can easily be intplemented. The bottom layer is formed by the Amoeba Block Services, responsible for implementing stable storage and repficated, highly available disk blocks. The next layer is formed by the Amoeba File Service which provides version management and concurrency control for tree-structured files. On top of this layer, the appficafions, ranging from databases to source code control systems, determine the structure of the file trees and provide an interface to the users

An Abort Mechanism for Nested Distributed Transactions

A transaction processing facility must have a mechanism for aborting transactions on request. This paper describes a mechanism for aborting transactions that can be arbitrarily nested and/or distributed. The mechanism consists of an "abort protocol" plus an adjustment to the commit protocol. The abort protocol locates and terminates as many of the transaction's operations as it can. If after the protocol has finished it is still possible that orphaned operations exist, then a simple check during the prepare phase of the commit protocol ensures that no orphan commits. The mechanism has many advantages: provided that the communication subsystem provides prompt failure detection, there will be no orphans: a site can abort unilaterally: there is little overhead on transaction-operation messages, and relatively few and relatively minor restrictions on the transaction facility: no information need be maintained in stable storage: and the abort protocol never blocks. The primary disadvantages of the mechanism are that the abort protocol must be synchronous, that it may over-abort in some cases, and that - if the communication subsystem does not provide prompt failure detection - there is no limit on the extent or lifetime of orphaned computations

Findings of a comparison of five filing protocols

Filing protocols are essential for the management and dissemination of shared information within computer systems. This is a survey of the current state of the art in filing protocols. Five popular filing protocols were selected and subjected to a rigorous comparison. FTAM, FTP, UNIX rep, XNS Filing, and NFS are compared in the following areas: exported interface, concurrency control, access control, error recovery, and performance. The coverage of background material includes a taxonomy and a brief history of filing protocols

Methodology for modeling high performance distributed and parallel systems

Performance modeling of distributed and parallel systems is of considerable importance to the high performance computing community. To achieve high performance, proper task or process assignment and data or file allocation among processing sites is essential. This dissertation describes an elegant approach to model distributed and parallel systems, which combines the optimal static solutions for data allocation with dynamic policies for task assignment. A performance-efficient system model is developed using analytical tools and techniques. The system model is accomplished in three steps. First, the basic client-server model which allows only data transfer is evaluated. A prediction and evaluation method is developed to examine the system behavior and estimate performance measures. The method is based on known product form queueing networks. The next step extends the model so that each site of the system behaves as both client and server. A data-allocation strategy is designed at this stage which optimally assigns the data to the processing sites. The strategy is based on flow deviation technique in queueing models. The third stage considers process-migration policies. A novel on-line adaptive load-balancing algorithm is proposed which dynamically migrates processes and transfers data among different sites to minimize the job execution cost. The gradient-descent rule is used to optimize the cost function, which expresses the cost of process execution at different processing sites. The accuracy of the prediction method and the effectiveness of the analytical techniques is established by the simulations. The modeling procedure described here is general and applicable to any message-passing distributed and parallel system. The proposed techniques and tools can be easily utilized in other related areas such as networking and operating systems. This work contributes significantly towards the design of distributed and parallel systems where performance is critical

Pyxis : um sistema de arquivos distribuido

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro TecnologicoEste texto apresenta o PYXIS, um sistema de arquivos distribuído portável com alto grau de paralelismo interno, desenhado para ser flexível no que diz respeito ao ambiente sobre o qual seus componentes são distribuídos, possibilitando sua execução em multicomputadores ou em redes de computadores. O projeto foi desenvolvido no Curso de Pós-Graduação em Ciências da Computação da Universidade Federal de Santa Catarina (CPGCC/UFSC) e deverá integrar um projeto coletivo das universidades federais de Santa Catarina (UFSC), do Rio Grande do Sul (UFRGS) e de Santa Maria (UFSM), que visa desenvolver um multicomputador e um ambiente para programação paralela sobre ele