libvirt users - Dec 2011 - Temporary use of disk space when deploying KVM with qcow2?

Hello,

I'm using libvirt to deploy a series of 7 KVM (in qcow2 format)
sequentially. The base image of the qcow2 is an ubuntu server.

The environment where i am doing this is a Live USB Ubuntu with a
persistence file (so that changes made remain).


So, my problem:

* If the persistence file (i.e. free disk space in the live ubuntu) is up
to around 1.5GB, the qemu process of launching the first one of the KVM
gets stuck, and a few seconds later an Ubuntu message pops up saying there
is no disk space left.

* If the persistence file is a bit bigger (100 MB more), it can launch the
7 KVM machines without any disk space problems.


This would suggest that during the deployment of one virtual machine, there
is a short period of time where a big amount of disk space (similar to the
size of the base image) is used (even if i am using qcow2 vms) and
afterwards released, so it can be used to launch the second vm, released,
used for the third, and so on.

If this is correct, i would like to know who is using that space, since my
intention would be to, if possible, redirect this temporary disk usage to a
RAM filesystem such as tmpfs, so that i don't need such a huge persistence
file in the USB.


I'm aware that this might be related to qemu-kvm rather than to libvirt
itself, but i can't find information about it and i would appreciate if
anyone could point me in the right direction. More details or clarification
can be provided if needed.

Best regards,
Jorge
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