170 likes | 181 Views
This article covers the consistency mechanisms in NFS and AFS network file systems, including client caching, write-through caching, callback lists, and session semantics.
E N D
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 • Other clients poll the server periodically for changes • No guarantees for multiple writers
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 + Simple and highly portable - May become inconsistent sometimes • Does not happen very often
AFS Illustrated Server cache: X Client A Client B
read X AFS Illustrated callback list of X client A Server cache: X Client A Client B read X
read X AFS Illustrated callback list of X client A Server cache: X Client A cache: X Client B read X
read X AFS Illustrated callback list of X client A Server cache: X Client A cache: X Client B read X
read X AFS Illustrated callback list of X client A client B Server cache: X Client A cache: X Client B read X
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 Illustrated Server cache: X Client A cache: X Client B cache: X write X, X X
X X AFS Illustrated Server cache: X Client A cache: X Client B cache: X close X
X X AFS Illustrated Server cache: X Client A cache: X Client B cache: X close X
AFS Illustrated Server cache: X Client A cache: X Client B cache: X close X
X AFS Illustrated Server cache: X Client A cache: X Client B cache: X open X
X AFS Illustrated Server cache: X Client A cache: X Client B cache: X open X