Hi Daniel, We have a problem with a build in Buildbot: https://internal.askmonty.org/buildbot/builders/kvm-rpm-centos7_0-x86_64/bui... + qemu-img create -b /kvm/vms/vm-centos7_0-x86_64-build.qcow2 -f qcow2 /dev/shm/vm-tmp-2302.qcow2 qemu-img: '' uses a qcow2 feature which is not supported by this qemu version: QCOW version 3 qemu-img: Could not open '/kvm/vms/vm-centos7_0-x86_64-build.qcow2' Failed to clone base image, aborting This failure happens on the build host `terrier'. I assume the problem is that the image was created on a machine with a newer KVM? The host terrier seems to have a rather old one: knielsen@terrier:~> kvm --version QEMU emulator version 0.13.0 (qemu-kvm-devel), Copyright (c) 2003-2008 Fabrice Bellard How do you think we should solve the problem? Should we upgrade terrier? Or should we alternatively make sure to create new images in a backward-compatible version (and re-create affected images) ? Also, another issue related to VM images. Our old images were created with rather small disk size. I noticed that some new images are created much larger, for example: $ qemu-img info /kvm/vms/vm-sid-amd64-build.qcow2 image: /kvm/vms/vm-sid-amd64-build.qcow2 file format: qcow2 virtual size: 40G (42949672960 bytes) disk size: 3.1G cluster_size: 65536 Format specific information: compat: 0.10 That is fine, I think, it is indeed annoying when we run out of space in a build VM. However, the reason I noticed this is because host bb02 ran out of space in /run/shm/ due to a 16 GB copy of this image. So when we use larger VM images, we cannot use the optimisation to have the temporary copies in ramdisk, lest we get disk full errors. If the virtual size is larger to (ram disk size) / (max_builds), then we need to disable using ramdisk for buildbot for that image. I will try to fix the config to not use ramdisk for existing images that have too large virtual size. But it is something to keep in mind for the future. - Kristian.