What is the NFSv3 mount "noac" option?

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Category:: ontap-9

Specialty:: nas

Last Updated:

Applies to

ONTAP 9

Answer

The noac option is a client side option available that disables attribute caching. This option is disabled by default. Unless there's a very specific reason to enable the noac option, NetApp Technical Support does not recommend enabling this option. The NFS attribute cache is a local cache of file and directory permissions. By disabling this cache, a new lookup has to occur each time to validate file and directory permissions. Expect an increase in IO operations and a decrease in performance if this option is enabled.

Additional Information

The "noac" mount option implies synchronous IO. For a write to be returned back to the application as complete, all data and filesystem metadata must have hit the NFS server.
The "actimeo=0" option does turn attribute caching off, however IO is still done asynchronously to the VFS layer, and the dirty page flush daemons on the client handle writing data out to the NFS server at a later time.