Recently we got a case where the explorer window on the Windows NFS client was freezing intermittently and the unfreezing while it trying to access NFS share. The NFS share was hosted on NetApp filer and hence was a multipath.

Initially we thought that it could be an issue with the multipath NFS share, which our NFS client is not known to handle very well. During the troubleshooting, we also update the NFS and RPC related drivers. But this did not resolve the issue.

Also we found that the issue was only happening if we access the share using UNC path. Mounting the UNC path to a drive and then accessing the share had no issues. We collect network traces and NFS tracing logs and found the below:

NFS traces indicated a problem TCP ports recycling in the Client for NFS driver. While using UNC access, the Client for NFS components needs to perform the mount/unmounts sequence for every access request as the persistent connection is not available. With the “Use Reserved Ports” option turned on, the TCP port pool available to use becomes limited and it increases the likelihood of TCP ports not being available to use. In those situations, the Client for NFS component keep trying until it get a ports that it can use and that can cause the freeze that you were experiencing.

Hence we suggested to disabled the “Use Reserved Ports” option under the security option for client for NFS properties. This increased the pool of available ports to use and mapped the NFS share to a drive letter so that we don’t waste CPU cycles and bandwidth with frequent mount/unmounts requests. SO, making the changes and restarting the Cleint for NFS service resolved the issue.