Sun Network File System

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Sun Network File System

• Presentation 3
• Group A4
• Sean Hudson, Syeda Taib, Manasi Kapadia

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Problem
How can physically distributed computers share a
file system?
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Solution
4
Background

• Developed by Sun.
• The NFS specification is platform independent
• Portable
• Operates in a heterogeneous environment.

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Fundamentals

• NFS was developed to allow a machine to mount a
  disk partition on a remote machine as if it were
  local.
• This allows for fast, seamless sharing of file
  across network.
• There is no global naming hierarchy.
• NFS allows any machine to be client or server.

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NFS Protocols

• Mount Protocol
• File Access Protocol
• Their functionality is defined as a set of Remote
  Procedure Calls (RPC).

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Mount Protocol
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Mount Protocol (cont.)

• After mount request, server returns a file handle
  (a key for further access).
• Mount operation changes only the users view.

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NFS Protocol
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Implementation

• Three major layers of NFS architecture
• System Call layer
• This handles calls like OPEN, READ, and CLOSE.
• Virtual File System (VFS) layer
• distinguishes local files from remote ones.
• NFS service layer
• implements the RPC calls.

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Schematic view of NFS
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Pathname Translation

• This is done by breaking the path into component
  names and performing a separate NFS lookup for
  every pair of component name and directory
  v-node.
• Lookups are performed remotely by the server.

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Performance

• Clients cache file attributes (i-nodes) and file
  data.
• Cached data blocks and directories are discarded
  periodically.
• When a cached file is open, the time it was last
  modified is checked at the server. If necessary,
  a new copy is brought from the server.

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Performance (cont.)

• Servers keep a cache to reduce disk I/O.
• Read-ahead caching
• Write-behind caching
• Periodically, modified cache blocks are written
  back to servers.

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Issues

• Synchronization of file accesses are not
  well-defined.
• Widely criticized for not implementing the UNIX
  semantics.

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Conclusion
NFS is a simple, popular and widely used file
system!
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References

• Casvant, Thomas and Singhal, Mukesh. Distributed
  Computing Systems. IEEE Press.
• Mullender, Sape. Distributed Systems. ACM Press.
• Pradeep, Sinha K. Distributed Operating Systems.
  IEEE Computer Society Press.
• Stallings, William. Operating Systems.
• Tanenbaum, Andrew. Distributed Operating Systems.