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NFS File Creation Cache Problems

Created by dave. Last edited by dave, 7 years and 206 days ago. Viewed 4,142 times. #2
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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.

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