I have some (6) boxes that have an NFS share mounted on which they write files. All run ubuntu 14.01 and the NFS server is a standard nfs-server from ubuntu packages. This works well.
However, when renaming files on the share by one system, it can take around half a minute before the other systems see the rename. Calling sync on the client after the rename doesn't help. Is this delayed write caching in action?