The error message “cannot create RPC client: clnttcp_create: RPC: Program not registered” in the context of VMware and VAAI (VMware vStorage APIs for Array Integration) indicates a problem with the communication between the ESXi host and the storage array. This error typically arises in situations involving network file systems (NFS) when trying to use VAAI features.

Here’s a breakdown of the issue and some steps you can take to troubleshoot and resolve it:

Understanding the Error

• RPC (Remote Procedure Call): This error points to an issue with establishing an RPC connection, which is crucial for operations that involve communication between your ESXi host and NFS servers or other network-based storage systems.

• Program Not Registered: This part of the error suggests that the NFS server or the targeted service does not recognize the RPC program requested by the ESXi host. It could mean that the necessary services or daemons on the NFS server are not running or properly configured to accept requests from the ESXi host.

Common Causes

1. VAAI NFS Plugin Issues: If the VAAI plugin for NFS is not installed, incorrectly installed, or not supported by the storage, it could lead to this error.

2. NFS Server Configuration: The NFS server may not be configured to support the necessary RPC services, or these services might not be running.

3. Network Issues: Problems with the network configuration, such as incorrect IP settings, subnet masks, or DNS issues, can prevent proper communication between the host and the storage.

Troubleshooting Steps

1. Verify VAAI Plugin Installation and Configuration:

• Check if the VAAI NFS plugin is installed on the ESXi host.

• Use the command esxcli storage nfs vaai status to check the status of VAAI on NFS datastores.

• Ensure the plugin is supported and properly configured according to your storage array’s documentation.

2. Check NFS Server Settings:

• Ensure that the NFS server is configured to support RPC connections for NFS.

• Verify that necessary services like nfs, nfslock, and rpcbind are running on the NFS server. You can check these services with commands like service nfs status on the server.

3. Network Configuration:

• Double-check the network settings including IP addresses, routes, and firewall configurations both on the ESXi host and the NFS server.

• Ensure there are no IP conflicts or incorrect gateway settings that might be causing communication issues.

4. Restart Services:

• Sometimes, simply restarting the NFS services on the server or the management agents on the ESXi host can resolve these issues. Use service nfs restart and service rpcbind restart on the NFS server.

• On the ESXi host, you can restart management network services or the entire hostd process if needed.

5. Consult Logs:

• Check the VMware ESXi logs and NFS server logs for any additional information that might help identify the specific cause of the problem. Logs can provide clues about what might be misconfigured or failing.

If the problem persists after these steps, it might be useful to consult with VMware support or the support services for your NFS server/storage array. They can offer more detailed guidance based on the specifics of your hardware and software environment.