In the vSphere docs (version 6.5 and earlier), in the section: vSphere API/SDK Documentation > vSphere Management SDK > vSphere Web Services SDK Documentation > vSphere Web Services SDK Programming Guide > Virtual Machine Configuration
The end of the first paragraph says:
However, do not use the VirtualMachine.ReconfigVM_Task call to create or add a disk.
Am I missing something, or is this a documentation error? Maybe it meant to say "while the machine is powered on"? (The following paragraphs talk about VM properties that can't be modified while the machine is on).