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

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

A12 Ex1 – Moving a shared volume NFS server: must change the export table 192.168.1.1 /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

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

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

Good luck! 1/13/2019