https://ovirt.mydomains/ovirt-engine/apidoc/#/ is not working (page is blank, has ovirt horizontal menu, but content is empty). You may mean the page https://ovirt.mydomains/ovirt-engine/apidoc/#/services/disk/methods/update It works for me, but the information I see on it seems insufficient (unusable) to me: update This operation updates the disk with the appropriate parameters. The only field that can be updated is qcow_version. For example, disk update can be done using the following request: PUT /ovirt-engine/api/disks/123 With a request body like this: <disk> <qcow_version>qcow2_v3</qcow_version> </disk> Since the backend operation is asynchronous, the disk element that is returned to the user might not be synced with the changed properties. I have HTTP Error 400: Bad Request Request syntactically incorrect. But syntax is OK: Ansible: --- - name: REST call w XML body uri: url: https://ovirt.{{ domain }}/ovirt-engine/api/disks/{{ diskid }} user: {{ user }} password: {{ password }} method: PUT validate_certs: no headers: Content-Type: "application/xml" #body_format: raw body: "{{lookup('file','put.xml')}}" register: result put.xml: <disk> <provisioned_size>18737418240</provisioned_size> </disk>