Converting a Raw Device Mapping (RDM) into virtual disk (VMDK).
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Converting a Raw Device Mapping (RDM) into virtual disk (VMDK).

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Article ID: 374087

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Updated On:

Products

VMware vSphere ESXi

Issue/Introduction

  • Both Virtual and Physical Compatibility mode RDMs can be converted into a VMDK
  • Virtual Compatibility mode RDMs can be converted while the VM is powered on
  • Physical Compatibility mode RDMs require either down time for the entire VM or just the RDM backing LUN.

Environment


VMware vSphere ESXi (All Versions)

 

Resolution

Converting Virtual RDM to VMDK:

--- Virtual mode RDM data can be migrated to a VMDK disk with Storage vMotion by selecting the Disk Format from Advance View. This operation can be performed when the Virtual machine is in both Powered on or Powered off state.

In the below example, the Hard Disk 3 (1 TB) which is a RAW LUN attached to the virtual machine as virtual compatibility RDM.

--- You can initiate the storage vMotion of the virtual machine with virtual RDM disks attached. To convert RDM to VMDK, You can use the Advanced option in Storage vMotion ->Change the disk format as “Thin or Thick” from the disk format drop down for the RDM disk, select the destination datastore and proceed with the storage vMotion.

--- Once storage vMotion is completed, virtual RDM disk will be converted to VMDK. 

Note: If you do not change the destination format to thick or thin provisioned for an RDM in the advanced section of the migration wizard, only the RDM mapping file will be migrated to the destination datastore.

 

Converting Physical RDM to VMDK:

 

Unfortunately converting a Physical RDM to a VMDK using Storage vMotion is not supported while the VM is Powered on

If you try to Change the Disk format of Physical RDM during Storage vMotion, you will receive error ” Virtual disk is mapped direct-access LUN in Physical compatibility mode; converting it to different disk type is not supported for  this operation”

There are two options for converting a Physical RDM to a VMDK

1. Convert the Physical RDM to a VMDK using Storage vMotion while the VM is Powered off 

As similar to Converting virtual RDM to VMDK using Storage vMotion with Disk format change option, you can convert the physical RDM to VMDK by changing Disk Format to Thick or thin during storage vMotion only when the virtual machine is Powered off.

2. Converting the Physical RDM to a VMDK using Storage vMotion while the VM is powered on requires the below 3 steps.

  1. Delete the Physical RDM Disk  from virtual machine (Delete from Disk option .  This will only delete RDM mapping file and  will not delete the data in the RDM.)
  2. Re-add the RDM LUN as virtual RDM disk
  3. Storage VMotion the virtual RDM disk by changing disk format to either Thick or Thin to convert RDM to VMDK.

Let’s go over this in more detail for a better understanding.

The virtual machine is attached to Physical RDM disk (1 TB) (Hard disk 3)

Remove the RDM disk from the virtual machine, and delete it from disk to ensure that the RDM mapping file is deleted. This will not delete the data in the RDM.

 

Re-add that RAW LUN to the virtual machine. Virtual Machine -> Edit Settings -> RDM Disk -> Add

Select the RAW LUN to add it as virtual RDM disk. Click ok.

Select the Compatibility Mode as “Virtual” and click Ok.

 

Once the same RAW Lun is added back as virtual RDM, you can select disk format as Thin or Thick during storage vMotion to convert Physical RDM disk to VMDK without powering off the virtual machine.

 

 

 

 

 

 

 

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