Since we cannot back up CD/DVD media devices attached to virtual machines, you would need to remove these devices to prevent the software from throwing this warning.
Remove a CD/DVD Drive from a VMware Virtual Machine
- In the Inventory panel within vSphere, select the virtual machine.
- Shut down the guest operating system and power off the virtual machine.
- In the Hardware section of the Summary tab, click the CD/DVD drive to remove and select Remove.
- Click Yes in the confirmation dialog box.
Remove a CD/DVD Drive from a Hyper-V Virtual Machine
- Open Hyper-V Manager. Click Start, point to Administrative Tools, and then click Hyper-V Manager.
- In the results pane, under Virtual Machines, select the virtual machine that you want to configure.
- In the Action pane, under the virtual machine name, click Settings.
- In the navigation pane (left pane), click the CD/DVD drive.
- On the DVD Drive page, click Remove
- Click OK.