Run VM from Overlay-Image

[Bernd Nachtigall]

Hi,

qemu: 3.1.1.1
qemu-kvm: 3.1.1.1

I want to multiplicate a existing VM in my KVM environment. The base VM
should not be changed from the volatile copy. So I choose:

# qemu-img create -f qcow2 -o base_img.qcow2 overlay1_img.qcow2

This create a valid virtual disk. I build a corresponding XML-file by
dump the XML from base VM and change name, uuid, MAC and set the new
disk. This makes a valid XML-file and I can start the new VM. No Problem.

But if I do this process twice it is not possible to run two of this
copied VMs at the same time. I get the message:
"internal error ... Failed to get "write" lock. Is another process using
the image [/path/to/VM/images/basis_img.qcow2]?"

But as far as I know it should be able to do this process more than once
to get multiple VM and these VMs should be able to run at the same time
because it should only read the base_img.cow2. I am wrong?

Bernd