RDM LUNs are not detected after being presented

Products

• VMware vSphere ESXi

Issue/Introduction

Unable to add new physical RDM VMDKs to virtual machines due to ESXi host path limit (4096)

• You are unable to add new physical Raw Device Mapping (RDM) VMDKs to virtual machines on a specific ESXi host.

• You observe leftover RDM pointer files remaining on the datastores from previously removed devices.

• The /var/log/vmkernel.log file on the affected ESXi host is flooded with warning messages similar to the following, indicating that new storage paths are being blocked:

vmkwarning: cpu14:2097637)WARNING: ScsiPath: 1247: The number of paths allocated has reached the maximum: 4096. Path: vmhba9:C0:T19:L1 will not be allocated. This warning won't be repeated until some paths are removed.

 vmkwarning: cpu43:2097639)WARNING: ScsiPath: 1247: The number of paths allocated has reached the maximum: 4096. Path: vmhba9:C0:T19:L1 will not be allocated.

Environment

vSphere ESX 7.X

vSphere ESX 8.X

and above

Cause

This issue occurs when the ESXi host reaches the maximum supported architectural limit of 4,096 allocated Fibre Channel paths. When this threshold is met, the host's storage daemon completely stops discovering and allocating newly assigned storage devices, preventing the addition of new RDM VMDKs.

Resolution

To allow new RDMs to be added, the total active path count must be reduced below the 4,096 threshold. Once the path count drops below this limit, the host will resume normal storage discovery operations.

 

Perform the following actions to reduce the path count and clean up your datastores:

1. Verify the current path saturation You can confirm the maximum device/path count has been saturated by running the following command via SSH on the affected ESXi host: esxcli storage core device list | grep -E "^naa|^eui|^mpx|^t10" | wc -l

2. Reduce Paths per LUN Review your SAN zoning and storage masking configurations. If a LUN is presented with an excessive number of paths (e.g., 8 paths), reduce the presentation to a more optimal number (e.g., 4 paths), provided it still satisfies your High Availability (HA) requirements.

3. Consolidate and Remove Unused Storage

• Use Storage vMotion to consolidate smaller LUNs where possible.

• Un-present any LUNs or datastores from the storage array that are no longer actively required by this specific host. Implementing these zoning changes will immediately free up logical paths.

 

Additional Information

Gemini said