Concept

Andrew File System

The Andrew File System (AFS) is a which uses a set of trusted servers to present a homogeneous, location-transparent file name space to all the client workstations. It was developed by Carnegie Mellon University as part of the Andrew Project. Originally named "Vice", "Andrew" refers to Andrew Carnegie and Andrew Mellon. Its primary use is in distributed computing. AFS has several benefits over traditional networked s, particularly in the areas of security and scalability. One enterprise AFS deployment at Morgan Stanley exceeds 25,000 clients. AFS uses Kerberos for authentication, and implements access control lists on directories for users and groups. Each client caches files on the local filesystem for increased speed on subsequent requests for the same file. This also allows limited filesystem access in the event of a server crash or a network outage. AFS uses the Weak Consistency model. Read and write operations on an open file are directed only to the locally cached copy. When a modified file is closed, the changed portions are copied back to the file server. Cache consistency is maintained by callback mechanism. When a file is cached, the server makes a note of this and promises to inform the client if the file is updated by someone else. Callbacks are discarded and must be re-established after any client, server, or network failure, including a timeout. Re-establishing a callback involves a status check and does not require re-reading the file itself. A consequence of the strategy is that AFS does not support large shared databases or record updating within files shared between client systems. This was a deliberate design decision based on the perceived needs of the university computing environment. For example, in the original email system for the Andrew Project, the Andrew Message System, a single file per message is used, like maildir, rather than a single file per mailbox, like mbox. See for handling shared databases. A significant feature of AFS is the volume, a tree of files, sub-directories and AFS mountpoints (links to other AFS volumes).

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Distributed shared memory 8DSM) is an abstraction of shared memory on a distributed memory machine. Hardware DSM systems support this abstraction at the architecture level; software DSM systems support the abstraction within the runtime system. One of the ...
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Clustered file system
A clustered file system is a which is shared by being simultaneously mounted on multiple servers. There are several approaches to clustering, most of which do not employ a clustered file system (only direct attached storage for each node). Clustered file systems can provide features like location-independent addressing and redundancy which improve reliability or reduce the complexity of the other parts of the cluster. Parallel file systems are a type of clustered file system that spread data across multiple storage nodes, usually for redundancy or performance.
Global file system
In computer storage, a global file system is a that can be accessed from multiple locations, typically across a wide-area network, and provides concurrent access to a global namespace from all locations. In order for a file system to be considered global, it must allow for files to be created, modified, and deleted from any location. This access is typically provided by a cloud storage gateway at each edge location, which provides access using the NFS or SMB network file sharing protocols.

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