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This Concept Map, created with IHMC CmapTools, has information related to: ch8 dist sun, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has client integration: the NFS client module's role is supplying an interface suitable for use by conventional application programs, it also emulates the semantics of the standard UNIX file system primitives precisely and is integrated with the UNIX kernel and not supplied as a library so that: 1 user programs can access files via UNIX 2 a single client module serves all of the user level processes 3 the encryption key used to authenticated user IDs passed to the server can be retained in the kernel, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has virtual file system: NFS provides access transparency: user programs can issue file operations for local or remote files without distinction, file identifiers used in NFS are called file handles, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has path name translation: UNIX file systems translate multi part file pathnames to i-node references in a step by step process whenever the open, creat or stat system calls are used, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has NFS summary: access transparency- the NFS client module provides an application programming interface to local processes that is identical to the local OS's interface location transparency- each client establishes a file name space by adding mounted directories in remote filesytems to its local name space mobility transparency- filesystems(in the UNIX sense, subtrees of files) may be moved between servers, but the remote mount tables in each client must then be updated separately to enable the clients to access the filesystem in its new location scalability- the published performance figures show that NFS servers can be built to handle very large real world loads in an efficient and cost effective manner file replication- read only file stores can be replicated on several NFS servers, but NFS does not support files replication with updates. hardware and OS heterogeneity- NFS has been implemented for almost every known OS and hardware platform and is supported by a variety of filing systems fault tolerance- the stateless and idempotent nature of the NFS file access protocol ensures that the failure modes observed by clients when accessing remote files are similar to those for local file access consistency- it provides a close approximation to one copy semantics and meets the needs of the vast majority of applications security- the need for security in NFS emerged with the connection of most intranets to the internet, the integration of kerberos with NFS was a major step forward efficiency- the measured performance of several implementations of NFS and its widespread adoption for use in stiuations that generate very heavy loads are clear indications of the efficiency with which the NFS protocol can be implemented, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has automounter: the automounter was added to the UNIX implementation of NFSin order to mount a remote directory dynamically whenever an empty mount point is referenced by a client, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has Mount service: the mounting of sub trees of remote filesystems by clients is supported by a separate mount service process that runs a user level on each NFS server computer, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has client caching: the NFS client module caches the results of read, write, getattr, lookup and readdir operations in order to reduce the number of requests transmitted to servers, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has NFS server interface: a simplified representation of the RPC interface provided by NFS version 3 servers, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has performance: -frequent use of getattr call in order to fetch timestamps from servers for cache validation, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has access control and authentication: the NFS server is stateless and does not keep files open on behalf of its clients, so the server must check the user's id against the file's access permission attributes afresh on each request, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has server caching: caching in both the client and the server computer are indispensable features of NFS implementations in order to achieve adequate performance, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has other optimizations: the SUN file system is based on the UNIX BSD fast file system which uses 8 kbyte disk blocks, resulting in fewer file system calls for sequential file access than previous UNIX systems, Sun Network File System (NFS): An industry standard for file sharing on local networks since the 1980s An open standard with clear and simple interfaces Closely follows the abstract file service model defined above Supports many of the design requirements already mentioned: transparency heterogeneity efficiency fault tolerance Limited achievement of: concurrency replication consistency security has securing NFS with kerberos: has become a standard for securing intranet servers against unauthorized access and imposter attacks, the kerberos scheme authenticates clients