rally-openstack/samples/tasks/scenarios/cinder/create-and-extend-volume.json

{
    "CinderVolumes.create_and_extend_volume": [
        {
            "args": {
                "size": 1,
                "new_size": 2
            },
            "runner": {
                "type": "constant",
                "times": 2,
                "concurrency": 2
            },
            "context": {
                "users": {
                    "tenants": 1,
                    "users_per_tenant": 1
                }
            }
        }
    ]
}