How practical would this idea be? I want to install KVM/qemu on a headless installation on my PC. I then to virtualize a windows installation and a linux installation, using VGA passthrough to give access to my graphics card. I would share the main drive with the guests for common storage, and have some way of switching between the two Vms.

Why?

What purpose would this serve that would not be served by shared storage and two discrete virtual machines?

It's because I have a PC with a single graphics card, so i can't run 2 at once. I think it would make it faster to switch between Os's if I had kvm save the state of the Vm i'm switching from and load the state of the vm i'm switching to.

I am writing this on a Laptop with a single graphics interface running Windows 7. I can run Linux in a VirtualBox VM with GUI on the console, or GUI via a VNC client.

On another PC I am running Windows XP in a VirtualBox VM on a Windows 7 machine.

I don't quite understand what you mean be "I can't run two at once".

I mean that I have a desktop PC with ONE discrete PCI graphics card. I will need the card for graphics programming. I will also need the card for windows gaming. only one OS can use the card at the time

You misunderstand how this works. Under virtualization your guest OS does not get to control ANY of your machine resources directly, to include the monitor. It gets a virtual monitor that you normally map to a window that can be raised, lowered, resized, etc. You CAN map it to the full screen, but that is under YOUR control.

I can run three virtual guests at the same time (though it drags performance to a crawl) and have no problem seeing all of them at once, one at a time, or background the lot and work at the hardware level.

The OP wants to use PCI passthrough to assign the video card (which is a PCI card) to a VM. This should make it unavailable to the host, thus the host must be headless. An interesting question.

I wonder:

• It's probably not possible to run two VMs using this card at the same time. Can you suspend one and run the other? Or does it need to be shut down entirely to release the VGA?
• The headless system will require a console. Serial console perhaps? Or is there a way to run a virtual terminal without a graphics card? And share it with VNC? What will you do if something breaks and you need console access?
• Would Xen be a better solution over KVM? Baremetal hypervisor, thinner than your headless installation. Or so I think; I have never tried it.

I was planning on writing a script or program to suspend one VM and run the other. Good point about releasing the VGA. I don't know

SSH and remote X from my laptop


I don't know. I think people are generally having more success with KVM, but it's worth looking into.

sure but what if networking can't be started on the server?

Then there would be value in extensive testing before going headless!

Also, in locking down the networking and NOT using (or even allowing installation of) NetworkManager.

I guess my best bet then is get a cheap graphics card to use with the host or dual-boot. I'll try that.