Comment 48 for bug 1847105

It works (as expected):

before:
4 0 17337 263 20 0 163108 4240 - Sl ? 0:47 \_ /usr/bin/qemu-img create -f qcow2 -o preallocation=falloc,compat=1.1,lazy_refcounts /var/lib/libvirt/images/ubuntu20.04.qcow2 26214400K

Now:
4 0 43901 263 20 0 163108 5436 - Sl ? 0:00 \_ /usr/bin/qemu-img create -f qcow2 -o preallocation=metadata,compat=1.1,lazy_refcounts /var/lib/libvirt/images/ubuntu20.04.qcow2 26214400K

Even without the change to libvirt it works (as that is a valid fix, but for a different use case).

And it is going much faster is on e.g. the ZFS based setup that was mentioned.