How to Configure RDM – Virtual Compatibility Disk

Posted By Rajesh Radhakrishnan March 11 2018

We have discussed about RDM in detail post and here I am going discuss about configure  RDM as a Virtual Compatibility disk to virtual machine.

There are two types of RDM Disks

Virtual Compatibility RDM Disksact same as a virtual disk file, including the use of snapshots. There are 2 ways we an create Virtual compatibility RDM disks , through CLI and  vSphere Web Client.

 Create Virtual Compatibility RDM Disks from CLI  

For this procedure we are using vmkfstools  , for this we should know the NAA ID of the physical LUN which we are going to add it as RDM disk to the virtual machine.

We can use the below command to find the NAA ID  by login to esxi through an ssh session

#esxcli storage core path list

Next change the directly  , cd towards  specific folder where you want to keep the RDM mapping file and execute the below command .

vmkfstools -r /vmfs/devices/disks/naa.XXXXXXXXXXXXXXXXXXXXXXXXX   diskname.vmdk


Note: RDM mapping file name will be helpful in many conditions such as maintenance of the LUN’s or disk.

Verify that there will be two available in side the folder where  diskname-rdm.vmdk  & diskname.vmdk using ” ls” commands from the folder.

Also you can check  by value   CreateType =”vmfsRawDeviceMap ”  inside the descriptor file

After creation of RDM mapping file using vmkfstools

  • Edit the VM properties -> Add Had disk -> Existing Hard Disk  ( From ESXi host )
  • Edit the VM properties -> Select “Existing Hard Disk” from the New Device drop-down Click on Add. ( From vCenter)

Browse RDM Mapping file – > Select the VMDK and Click Save  / Ok .

RDM disk appear as similar to below and click ok to take effect .

Next Login to the machine and Check the RDM is visible inside the GOS or not

Create Virtual Compatibility RDM Disks using vSphere Web Client

login to vCenter Server using vSphere Web Client or ESXi Host Web UI.

Select the virtual machine in the vCenter Server inventory -> Edit Settings. Select RDM Disk from the New Device Dropdown

Select the required  LUN to create it as RDM disk in the virtual machine and Click on Ok.

Select or Change   compatibility Mode to “Virtual” and also you can specify the location of the RDM Mapping file. You can choose either store with the virtual machine or select any specific datastore. Click OK.

Now login to the virtual machine and verify the 100 GB uninitialized RDM  , you can  create a partition on the attached RDM  disk an start using that .