10.2 THE CODA FILE SYSTEM Vrije Universiteit （10.2 sccp CODA文件系统）.pdfVIP

604 DISTRIBUTED FILE SYSTEMS CHAP. 10 10.2 THE CODA FILE SYSTEM Our next example of a distributed file system is Coda. Coda has been developed at Carnegie Mellon University (CMU) in the 1990s, and is now integrated with a number of popular UNIX-based operating systems such as Linux. Coda is in many ways different from NFS, notably with respect to its goal for high availability. This goal has led to advanced caching schemes that allow a client to continue operation despite being disconnected from a server. Overviews of Coda are described in (Satyanarayanan et al., 1990; Kistler and Satyanarayanan, 1992). A detailed description of the system can be found in (Kistler, 1996). 10.2.1 Overview of Coda Coda was designed to be a scalable, secure, and highly available distributed file system. An important goal was to achieve a high degree of naming and loca- tion transparency so that the system would appear to its users very similar to a pure local file system. By also taking high availability into account, the designers of Coda have also tried to reach a high degree of failure transparency. Coda is a descendant of version 2 of the Andrew File System (AFS), which was also developed at CMU (Howard et al., 1988; Satyanarayanan, 1990), and inherits many of its architectural features from AFS. AFS was designed to support the entire CMU community, which implied that approximately 10,000 worksta- tions would need to have access to the system. To meet this requirement, AFS nodes are partitioned into two groups. One group consists of a relatively small number of dedicated Vice file servers, which are centrally administered. The other group consists of a very much larger collection of Virtue workstations that give users and processes access to the file system, as shown