Uses time stamps client sends mod time stamp to

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Unformatted text preview: ith the master copy? Client-initiated approach • Client initiates a validity check. • Uses time-stamps – client sends mod time stamp to server for block B • Network File System (NFS) Server-initiated approach • Server records, for each client, the (parts of) files client is caching. • When server detects a potential inconsistency, it must react (notify the clients). • Andrew File System (AFS) Server Server type Stateful vs. Stateless Stateful – retains per client state between invocations Stateless – does not Stateless – more resilient Stateful Stateful File Service Mechanism. • Client opens a file. • Server fetches information about the file from its disk, stores it in its memory, and gives the client a connection identifier unique to to the client and the open file; records offset, etc. • Identifier is used for subsequent accesses until the session ends. • Server must reclaim the main-memory space used by clients who are no longer active. Stateful Stateful File Service Benefits? Stateless Stateless File Server Avoids state information by making each request selfcontained. read (file, offset, buffer) Each request identifies the file and position in the file. No No need to establish and terminate a connection by open and close operations. The Network File The Network File System (NFS) An implementation and a specification of a software system for for accessing remote files across LANs (or WANs) Orig. implementation part of the SunOS operating system - unreliable datagram protocol - Ethernet - Heterogeneous architectures: handle format differences - 10-100 clients NFS NFS...
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