Once a file is locked over NFS, it turns off all local memory caching on the file (which means every thing that is done to the file now happens over the remote NFS link -- read slow) until _all_ processes that had the file open close (even after the lock has been released). You may be seeing an 18 second delay because the file is large and NFS is using network mode instead of local cache mode to open and read the data. How big is the file and how long does it take to copy the entire file to the server the B process is running on? This is one of the major issues with NFS that vendors like NetAPP would have you ignore.