NFS File Creation Cache Problems

Problem

If I create a file on an nfs-mounted filesystem on one machine, the file may not be immediately visible to another machine looking at the same nfs-mounted filesystem.

In our case this happened with a compute farm environment, where a job was dispatched to a remote machine to write some file, then when that job finished the dispatching machine tried immediately read that file. This would regularly fail and the immediate work-around was a sleep(10) step in between the dispatched-job-finish and the subsequent read-the-created-file step.

Solution

$ man nfs
[...]

     lookupcache=type
         This option dictates how directories and files  should  be  cached  when  they  are
         accessed  --  i.e.  "looked  up"  -- on the server. A lookup can be either positive
         (directory/file was found) or negative (directory/file was not found);  both  types
         of lookups can be cached.

         By  default,  both  positive  and  negative lookups are cached ( lookupcache=all ).
         lookupcache=pos prevents negative lookups from being cached, while lookupcache=none
         prevents all lookups from being cached.

         Note:  lookupcache=none  can  adversely affect performance, but may be necessary if
         shared files created or deleted on the server need to be immediately visible to any
         applications running on NFS clients.

I added the option lookupcache=pos to the automount options for this filesystem and the problem went away.

Availability

This appears to be added for the RedHat/CentOS 5.4 release cycle and should be available in those or later releases.