I am unable to create disk using JSON however the same query in XML works great. In Json I get the following message back: { "detail": "For correct usage, see: https://ov1.butterflyit.com/ovirt-engine/apidoc#services/disks/methods/ad...;, "reason": "Request syntactically incorrect." } Both use POST /ovirt-engine/api/disks and the content-type is either application/json or application/xml Here is the request in JSON: { "id": "866770c3-acf9-4f67-b72c-05ed241908e4", "name": "mydisk", "description": "test disk", "bootable": false, "shareable": true, "provisioned_size": 10240000000, "interface": "virtio", "format": "cow", "storage_domains": { "storage_domain": { "name": "VMS" } } } And here it is in XML <disk id="866770c3-acf9-4f67-b72c-05ed241908e4"> <bootable>false</bootable> <name>mydisk</name> <description>test Drive</description> <interface>virtio</interface> <provisioned_size>10240000000</provisioned_size> <format>cow</format> <storage_domains> <storage_domain> <name>VMS</name> </storage_domain> </storage_domains> </disk>