Thank you for input.  Finally I found the issue is "NFS mounts from unprivileged ports". The issue was resolved.  Hope  the following resolution can help the other ones.  On a classical Unix setup we call this insecure NFS export option, on the DellEMC Isilon site I found the following article: "NFS mounts from unprivileged ports". This should be easy to turn on and off, See:  [URL]   //////////////////////////////////////////////////////////////////  Procedure  OneFS 7.2.X using Userspace NFS The NFS service has been moved from the operating system kernel space into user space. The configuration of kernel space tuning via sysctl no longer applies and has moved into gconfig. To allow NFS mounts from unprivileged ports: By default, registry.Services.lwio.Parameters.Drivers.nfs.NFSPrivPort is 1, unprivileged port is not allowed. Restart NFS service  NOTE: You have to restart NFS on every Isilon node.  Kernel Space NFS  The setting is managed by a sysctl in kernel space.  
Our Isilon X400 was just upgraded from V7.1.1.0 to V8.0.0.4. After upgrading,  virtual machines on VMware can not access their NFS mount from Isilon, but physical server can still access their NFS mount from Isilon. Default Unix NFS export options normally do not include *insecure*, it is set as "secure" by default.  This is the possible reason. How to enable "insecure" under OneFS?   I have completed the following steps but didn't resolve the problem:  On OneFS GUI:    Protocal -->NFS -->Export Settings --> Security Flavors --> Use Custom --> check UNIX (system).  Can anybody provide suggestion? 
NFS mount can not be accessed by virtual machine after upgrading OneFS from 
V7.1.1.0 to V8.0.0.4