Consistency in nfs and afs
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Consistency in NFS and AFS. Network File System (NFS). Uses client caching to reduce network load Built on top of RPC. Server cache: X. Client A cache: X. Client B cache: X. NFS Weak Consistency Protocol. Write-through caching: A write updates the server immediately

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Consistency in NFS and AFS

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Consistency in nfs and afs

Consistency in NFS and AFS


Network file system nfs

Network File System (NFS)

  • Uses client caching to reduce network load

  • Built on top of RPC

Server cache: X

Client A cache: X

Client B cache: X


Nfs weak consistency protocol

NFS Weak Consistency Protocol

  • Write-through caching: A write updates the server immediately

  • Other clients poll the server periodically for changes

  • No guarantees for multiple writers


Andrew file system afs

Andrew File System (AFS)

  • Developed at CMU

  • Design principles

    • Files are cached on each client’s disks

      • NFS caches only in clients’ memory

    • Callbacks: The server records who has the copy of a file

    • Write-back cache on file close. The server then tells all clients that own an old copy.

    • Session semantics: Updates are only visible on close


Nfs summary

NFS Summary

+ Simple and highly portable

- May become inconsistent sometimes

  • Does not happen very often


Afs illustrated

AFS Illustrated

Server cache: X

Client A

Client B


Afs illustrated1

read X

AFS Illustrated

callback list of X

client A

Server cache: X

Client A

Client B

read X


Afs illustrated2

read X

AFS Illustrated

callback list of X

client A

Server cache: X

Client A cache: X

Client B

read X


Afs illustrated3

read X

AFS Illustrated

callback list of X

client A

Server cache: X

Client A cache: X

Client B

read X


Afs illustrated4

read X

AFS Illustrated

callback list of X

client A

client B

Server cache: X

Client A cache: X

Client B

read X


Afs illustrated5

read X

AFS Illustrated

callback list of X

client A

client B

Server cache: X

Client A cache: X

Client B cache: X

read X


Afs illustrated6

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

write X, X  X


Afs illustrated7

X  X

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

close X


Afs illustrated8

X  X

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

close X


Afs illustrated9

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

close X


Afs illustrated10

X

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

open X


Afs illustrated11

X

AFS Illustrated

Server cache: X

Client A cache: X

Client B cache: X

open X


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