1. Overview
Assignment 12: solution
Distributed file systems
1/13/2019

2. A12 – AFS vs. NFS
AFS
NFS
Common name space for all cells (/afs/ethz.ch, /afs/cmu.edu)
Different mount points (nfs.ethz.ch:/export/dir/)
Automatic tracking of cell databases
Mount points set by administrators
Client caching to reduce network load; callbacks to maintain cache consistency
No local file caching
Suitable for wide-area
Suitable for local-area
Reconfiguration
Server reconfiguration
No user impact; files remain accessible during moves
Server and client reconfiguration
Users loose access to files (mount points need to be reconfigured)
1/13/2019

3. A12 Ex1 – Moving a shared volume
NFS
server: must change the export table /export/disk(ro)
client: update the NFS imports server:/export/disk /mnt/nfs nfs defaults 0 0
unmount and remount
AFS
move the volume, re-register it
no changes on client
1/13/2019

4. A12 Ex2 – Simultaneous accesses
NFS
every change is sent (via RPC) to the server
every change is visible
AFS
changes are committed at the end, when sync or close is called
Consequences:
NFS: changes are done whenever they happen
AFS: only one change at the end
1/13/2019

5. A12 Ex3 – Immutable files send new file to server only at commit time
caching possible
no coherency mechanisms needed
data replication possible without conflicts
1/13/2019

6. Good luck!
1/13/2019