# openshift-virt CBT https://lwn.net/Articles/837053/ > Hi Kevin. I am trying to test out qemu bitmaps with external data files. > I found your patches > <https://patchwork.kernel.org/project/qemu-devel/patch/20190227172256.30368-16-kwolf@redhat.com/> > but > not any documentation on how to use the 'data-file' option to create a > qcow2 file that will work in this manner. Could you provide an example > please? To create both the qcow2 file and its data file, you can use a command line like this: qemu-img create -f qcow2 -o data_file=/tmp/data.img /tmp/test.qcow2 8G