DFS（distributed file system）

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A clustered file system is a file system 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.

distributed file system是clustered file system 的一种：

Distributed file systems do not share block level access to the same storage but use a network protocol. These are commonly known as network file systems, even though they are not the only file systems that use the network to send data. Distributed file systems can restrict access to the file system depending on access lists orcapabilities on both the servers and the clients, depending on how the protocol is designed.

The difference between a distributed file system and a distributed data store is that a distributed file system allows files to be accessed using the same interfaces and semantics as local files - e.g. mounting/unmounting, listing directories, read/write at byte boundaries, system‘s native permission model. Distributed data stores, by contrast, require using a different API or library and have different semantics (most often those of a database).

Design goals

Distributed file systems may aim for "transparency" in a number of aspects. That is, they aim to be "invisible" to client programs, which "see" a system which is similar to a local file system. Behind the scenes, the distributed file system handles locating files, transporting data, and potentially providing other features listed below.

• Access transparency is that clients are unaware that files are distributed and can access them in the same way as local files are accessed.
• Location transparency; a consistent name space exists encompassing local as well as remote files. The name of a file does not give its location.
• Concurrency transparency; all clients have the same view of the state of the file system. This means that if one process is modifying a file, any other processes on the same system or remote systems that are accessing the files will see the modifications in a coherent manner.
• Failure transparency; the client and client programs should operate correctly after a server failure.
• Heterogeneity; file service should be provided across different hardware and operating system platforms.
• Scalability; the file system should work well in small environments (1 machine, a dozen machines) and also scale gracefully to huge ones (hundreds through tens of thousands of systems).
• Replication transparency; to support scalability, we may wish to replicate files across multiple servers. Clients should be unaware of this.
• Migration transparency; files should be able to move around without the client‘s knowledge.

History

The Incompatible Timesharing System used virtual devices for transparent inter-machine filesystem access in the 1960s. More file servers were developed in the 1970s. In 1976Digital Equipment Corporation created the File Access Listener (FAL), an implementation of the Data Access Protocol as part of DECnet Phase II which became the first widely used network file system. In 1985 Sun Microsystems created the file system called "Network File System" (NFS) which became the first widely used Internet Protocol based network file system.^[3] Other notable network file systems are Andrew File System (AFS), Apple Filing Protocol (AFP), NetWare Core Protocol (NCP), and Server Message Block(SMB) which is also known as Common Internet File System (CIFS).

Examples

• GFS (Google Inc.)
• HDFS (Apache Software Foundation)
• IFS (EMC Isilon)
• Ceph (Inktank, Red Hat)
• MooseFS (Core Technology / Gemius)
• Windows Distributed File System (DFS) (Microsoft)
• BeeGFS (Fraunhofer)
• GlusterFS (Red Hat)
• Lustre
• Ibrix

Reference： http://en.wikipedia.org/wiki/Clustered_file_system#Shared-disk_.2F_storage_area_network

DFS（distributed file system）

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原文地址：http://www.cnblogs.com/HollyL/p/4286826.html