Mapping Windows Drives to RDMs in VMware ESX/ESXi

It can be confusing when trying to identify the RDM that correlates to a Windows drive. To give you some context, let’s assume you receive a request to increase the K:\ drive on a SQL Server because it has run out of free space. You navigate to the VM to find the RDM in question but are faced with this:


So which disk needs to be expanded? To identify the correct disk, log onto the VM in question and fire up Disk Management.

Locate the drive in question, for this example we are using the K:\ drive:


Right-click on the disk and click on Properties:


In the General tab in the Location section make a note of the details, in our example above, the information we need is Bus Number 0, Target Id 6.

Windows uses a 0 for the Bus Number whereas VMware uses a 1. So for our example, Bus Number 0, Target Id 6 correlates to an RDM with a SCSI ID of 1:6.

Locate the VM using the vSphere client and go into the settings and locate the Hard Disk that has a SCSI ID of 1:6, see below:


We can see that Hard Disk 8 has a SCSI ID of 1:6. The next would be to click on Manage Paths and note down the naa #, which is highlighted below:


Using that #, naa.600601609aa02e004d7489a8adbce211, you can identify the LUN in question on the storage array and increase it according to requirements.

To cement this knowledge, lets use another example. If the Windows drive had the following the following info, Bus Number 0, Target Id 8, the RDM disk will have a SCSI ID of 1:8.

Note: Windows also uses the Bus Number 0 for SCSI controller 0, therefore do not confuse the disks on SCSI controller 0, with RDM disks on SCSI controller 1.