Lectures notes for 2010 - KTH

NFS Statelessness
NFS is designed to be stateless
• the server does not keep track of what clients are accessing which files
• there are no open or close procedures; just LOOKUP
• being stateless simplifies server crash recovery
• clients don’t know if the server crashes
• only the client maintains state
Most procedures (GETATTR, STATFS, LOOKUP, READ, WRITE, READIR)
are idempotent (i.e., can be executed more than once by the server with the same
result).
Some (CREATE, REMOVE, RENAME, SYMLINK, MKDIR, RMDIR) are not.
SETATTR is idempotent unless it is truncating a file.
To handle non-idempotent requests - most servers use recent-reply cache,
checking their cache to see if they have already performed the operation and
simply return the same value (as before).
Maguire Network File System (NFS) 5: 68 of 77
maguire@kth.se 2010.03.21 Internetworking/Internetteknik