Every once in a while, you’ll come across a customer who has a LUN that is physically passed through to vSphere using Raw Device Mapping(RDM).  I usually discover these when we are migrating or a customer makes some other change.  I have been asked recently on the best way to convert a physical RDM to a regular VMDK, so here are the steps (sorry no pics, keep bugging me and I may find time to take some screenshots in the lab)

Here are the steps to convert a pRDM to vRDM then to a VMDK.

First, make sure no one is accessing the pRDM. (pretty important, we are going to remove it from the VM)

In the vSphere client, right click the virtual machine and select edit settings.

Find the RDM you wish to remove, highlight it and select remove., then check “remove from virtual machine” and click OK.

Allow the reconfiguration of the VM to complete.

Then right click the VM and select edit settings.  Click Add.  Select hard disk and click next.  Select Raw Device Mappings and click next

Select the correct LUN and click Next.  Click Next again. Select Virtual and click Next. Click Next again. Click Finish. Click OK.

Allow the reconfiguration of the VM to complete.

Now that the pRDM is a vRDM, you can svMotion it to a VMDK.

Right click the VM and select Migrate.  Select Change Datastore and click Next.  Click Advanced.

Find the RDM and click where it says browse.  Select a Datastore and click OK. Now click where it says disk format and select Thick provision and click Next.

Click Finish.

The disk will now clone to a thick provisioned VMDK.

You can also migrate from a pRDM to a VMDK if you power off the VM and use migrate, however the VM will be unusable during the whole migration, where with this method, access to the RDM is only suspended during the conversion from Physical to Virtual.  After it is reattached, you can svMotion it while it is being used.