Comment 3 for bug 1285240

100% agree that it's far from clear Greg, thanks for the report. The reason why it's saying "volume is required" is that the json looks like { ... "volume": { "size": "5" } }. so if the "volume" field isn't present, the apischema validation runs (see https://github.com/openstack/trove/blob/master/trove/common/apischema.py#L191-L192) and correctly reports that "volume" isn't present.

the only way this can be enhanced is in python-troveclient, via an error-message rewrite, which is a bit hacky.