Relocating RDM Pointer Files to a New Datastore

Products

• VMware vCenter Server

Issue/Introduction

This article provides instructions for moving Raw Device Mapping (RDM) pointer files from one datastore to another. This is often necessary during storage decommissioning or datastore housekeeping to ensure VM availability when a source datastore is unmounted.

Symptom

• A virtual machine (VM) fails to power on after a datastore is unmounted or deleted.
• Error: "Virtual disk 'Hard disk #' is a mapped direct-access LUN that is not accessible."
• RDM pointer files are split across multiple datastores, hindering storage consolidation.

Environment

• VMware vSphere ESXi 8.x
• VMware vCenter Server

Cause

The RDM mapping file (pointer) resides on a datastore that has been unmounted or decommissioned, even though the raw LUN data remains intact. vSphere cannot locate the descriptor file required to map the LUN to the VM.

Resolution

To safely relocate mapping files to a new datastore without affecting raw LUN data, follow these steps:

1. Shut down the guest virtual machine where the RDM is currently attached.
2. Remove the RDM from the virtual machine:
   
   
   1. Select the VM, go to Edit Settings.
   2. Select the RDM hard disk and click Remove.
   3. Select Delete from disk to destroy the pointer on the old datastore (this does not affect raw LUN data).
3. Add the LUN back to the virtual machine as a new RDM:
   
   
   1. In Edit Settings, select Add New Device > RDM Disk.
   2. Select the target LUN from the list.
   3. In the Datastore selection, choose the new destination datastore for the mapping file location.
   4. Select Physical compatibility mode.
4. Verify the path via CLI if needed using the command: ls -alh /vmfs/devices/disks/vml.#### 

Additional Information

• For more details on RDM management, see Migrating VMs with RDMs.
• For the latest updates, see Download Broadcom products and software.
• To speak with a customer representative see Contact Support.