oVirt supports this from the web interface but it is a very cumbersome and slow process. It also breaks often for obscure reasons in my experience. Using the SSH console, you can create your image directly on your backup server using NFS or whatever you are used to.
I learned how to do this from this web resource: https://coderwall.com/p/ei2x4g/export-ovirt-vm-to-qcow2-image-file
Figure out location disk images of your VM
You first need to figure out wich logical volumes are associated with your VM. Log in into the oVirt host where your vm of interest is running.
# virsh --readonly domblklist myvm
Target Source
------------------------------------------------
hdc -
vda /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/8b0df65f-5ebf-4a86-9329-4458064ee0b1/8675239b-8ebc-4174-8196-f3c567e8b2d5
vdb /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/dbe06a1d-ff79-4486-9266-30c75f7d7fd0/9c6334eb-389a-4794-ab54-20a29a667ec2
In this case the machine has two disks we want to migrate.
The ‘/rhev’ sources are actually links to block devices:
# ls -alt /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/8b0df65f-5ebf-4a86-9329-4458064ee0b1/8675239b-8ebc-4174-8196-f3c567e8b2d5
lrwxrwxrwx. 1 vdsm kvm 78 Feb 25 2019 /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/8b0df65f-5ebf-4a86-9329-4458064ee0b1/8675239b-8ebc-4174-8196-f3c567e8b2d5 -> /dev/b4525332-c435-4d75-9785-4f23ad976d8b/8675239b-8ebc-4174-8196-f3c567e8b2d5
# ls -alt /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/dbe06a1d-ff79-4486-9266-30c75f7d7fd0/9c6334eb-389a-4794-ab54-20a29a667ec2
lrwxrwxrwx. 1 vdsm kvm 78 Feb 25 2019 /rhev/data-center/mnt/blockSD/b4525332-c435-4d75-9785-4f23ad976d8b/images/dbe06a1d-ff79-4486-9266-30c75f7d7fd0/9c6334eb-389a-4794-ab54-20a29a667ec2 -> /dev/b4525332-c435-4d75-9785-4f23ad976d8b/9c6334eb-389a-4794-ab54-20a29a667ec2
Alternative way to figure out disk device
You could also figure out the disk ID from the oVirt web console (or database) and then directly search it in the /rhev/data-center/ folder on any oVirt host. Navigate to ‘Storage > Disks’ to see the list of disks and their ID’s.
Activate the logical volumes
Now with the VM powered down:
# lvchange -ay /dev/b4525332-c435-4d75-9785-4f23ad976d8b/8675239b-8ebc-4174-8196-f3c567e8b2d5
# lvchange -ay /dev/b4525332-c435-4d75-9785-4f23ad976d8b/9c6334eb-389a-4794-ab54-20a29a667ec2
Might save you the trouble to spin up the VM to learn where it’s disks are located…
Create image files from these block devices
Handy about this procedure is you can save your disk file directly on the storage of your choice. Just mount them in some way on your oVirt host (NFS, SSHFS, rclone, …).
# cd /mnt/storage
# qemu-img convert -p -O qcow2 /dev/b4525332-c435-4d75-9785-4f23ad976d8b/8675239b-8ebc-4174-8196-f3c567e8b2d5 myvm.vda.qcow2
# qemu-img convert -p -O qcow2 /dev/b4525332-c435-4d75-9785-4f23ad976d8b/9c6334eb-389a-4794-ab54-20a29a667ec2 myvm.vdb.qcow2
Deactivate logical volumes
# lvchange -an /dev/b4525332-c435-4d75-9785-4f23ad976d8b/8675239b-8ebc-4174-8196-f3c567e8b2d5
# lvchange -an /dev/b4525332-c435-4d75-9785-4f23ad976d8b/9c6334eb-389a-4794-ab54-20a29a667ec2