NFS Mount failed and now it says `Device not configured`
Restart NFS without Rebooting

Issue the following command in Terminal:

sudo nfsd restart


This has the effect of stopping the NFS daemon, starting it back up, rereading your config and processing what's in your /etc/exports

OS X Disconnecting from NFS

Try this: 

find . -name ._* | xargs rm on the R-Pi  in the directory that gets mounted.  That will remove any of the hidden "_filename" files that OS X creates when going through a directory

Based on this Apple Support Forum with similar symptoms:  https://discussions.apple.com/thread/2733032?start=0&amp;tstart=0