Defrag for SQL Servers inside a Virtual Machine?

sorry for asking here, since there's no forum for Virtual Server

My question is

We have 2 SQL Server instances on 2 Virtual Machine/Servers (say VM1 and VM2), which resides on a real physical machine (say A)

Is there point in defragging VM1 or VM2's hard drive at all?

or should I just defrag on the physical machine A?

You want to make sure the VMs are down (stopped) then defrag the physical machine. That would be all you need.|||

that's what I thought anyway, first time I defragged without shutting VMs down, I got a blue screen on 1 VM

second time I defragged still without shutting VMs down, everything went smoothly

I guess it's safer to shut down the VMs anyway

Thanks for the answer