'Extend DISCO volume.'

def volumeExtend(self, vol_id, size):

    params = {'volumeSize': six.text_type(size), 'volumeId': six.text_type(vol_id)}
    data = json.dumps(params, sort_keys=True, indent=4, separators=(',', ':    '))
    request = ('%(req_prefix)s/volume/extend' % self.prefix_var)
    r = requests.put(request, data, headers=self.req_headers)
    return r.json()
