Managing Attribute Caching

The file metadata information that NFS clients read using the NFS GETATTR call can be read from a cached copy of this information stored on the NFS client instead of from the NFS server.

Note 

Some applications such as Oracle's 9iRAC technology require you to disable attribute caching, so the noac option discussed next may not be available to improve NFS client performance under all circumstances.

To see the difference in performance between GETATTR operations that use the NFS server and GETATTR calls that use cached attribute information, mount the NFS filesystem with the noac option on the NFS client and then run a typical user application with the following command (also on the NFS client):

 #watch nfsstat -c 

Watch the value for "getattr" on this report increase as the application performs GETATTR operations to the NFS server. Now remove the noac option, and run the database report again. If the change in value for the getattr number is significantly lower this time, you should leave attribute caching turned on.

Note 

Most applications with I/O-intensive workloads will perform approximately 40 percent more slowly when attribute caching is turned off.

The performance of the attribute caching is also affected by the timeout values you specify for the attribute cache. See the options acregmin, acregmax, acdirmin, acdirmax, and actimeo on the nfs man page.

Note 

Even with attribute caching turned on, the NFS client (cluster node) will remove attribute information from its cache each time the file is closed. This is called close-to-open or cto cache consistency. See the nocto option on the nfs man page.