'Finds the controller on which the Dell volume is active.
There can be more than one Dell backend controller per Storage center
but a given volume can only be active on one of them at a time.
:param scvolume: Dell backend volume object.
:returns: Active controller ID.'

def _find_active_controller(self, scvolume):

    actvctrl = None
    volconfig = self._get_volume_configuration(scvolume)
    if volconfig:
        controller = volconfig.get('controller')
        actvctrl = self._get_id(controller)
    else:
        LOG.error('Unable    to    retrieve    VolumeConfiguration:    %s', self._get_id(scvolume))
    LOG.debug('_find_active_controller:    %s', actvctrl)
    return actvctrl
