Removing snapshots from virtual machines with shared physical mode RDMs

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

• Snapshots are not supported on virtual machines (VMs) using physical compatibility mode Raw Device Mappings (RDMs) or SCSI bus sharing.
• If snapshots were inadvertently created (e.g., during a backup operation or mode change), they must be removed to ensure disk stability and allow configuration changes.
• This article provides the procedure to safely consolidate snapshots in a shared storage environment.

Environment

VMware vCenter Server
VMware vSphere ESXi

Cause

In Physical compatibility mode VMware-native snapshots and advanced migration features are not supported. This is because the hypervisor passes almost all SCSI commands directly to the hardware without intercepting them (with the exception of LUN Report).

However, in Virtual compatibility mode, the hypervisor intercepts these commands and manages the RDM just like a standard virtual disk file. This unlocks native capabilities, allowing you to successfully use snapshots and cloning.

For VMs with physical RDM that do have snapshots, it needs to be either removed or consolidated to ensure the VM continues to work as expected.

Resolution

Perform the following steps to consolidate and remove snapshots:

• Power off all virtual machines sharing the physical RDM.
• Edit settings for each VM and record the SCSI controller and Target ID for the RDM.
• Remove the RDM from all affected VMs. Select "Remove Device" from virtual machine.
  • Note: Do not select "Delete files from disk" so that the data on the physical LUN is preserved. If the data also needs to be removed for the VMs, only then select this option.
• Set the SCSI Bus Sharing to None on the SCSI controller.
• Consolidate snapshots:
  
  • Right-click the VM > Snapshots > Consolidate.
  • If "Consolidate" is unavailable, go to Manage Snapshots and select Delete All.
    • Note: Other option to consolidate snapshot on the VM includes performing a storage vMotion or clone a new VM from the previous one.
• Re-add the RDM to the primary VM:
  
  • Select Add New Device > RDM Disk.
  • Choose the original LUN and set the compatibility mode to Physical.
  • Assign it to the original SCSI ID.
• Re-add the RDM to the secondary VMs as an Existing Hard Disk.
• Power on the virtual machines.

Additional Information

For more information, please refer the below articles:

• Switching a raw data mapping (RDM) between physical and virtual compatibility modes in ESX/ESXi
• Create vSphere Virtual Machines with RDMs