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.