Information
Ensure no device is connected to a virtual machine if it is not required. For example, floppy, serial, and parallel ports are rarely used for virtual machines in a data center environment, and CD/DVD drives are usually connected only temporarily during software installation.
Solution
For each virtual machine do the following:
From the vSphere Client, right-click the Virtual Machine and go to "Edit Settings".
Select the CD/DVD drive and uncheck "Connected" and "Connect at power on" and remove any attached ISOs.
or
From a PowerCLI command prompt while connected to the ESXi host or vCenter server, run the following command:
Get-VM "VM Name" | Get-CDDrive | Set-CDDrive -NoMedia