'Creates any appropriate replications for a given volume.
:param api: Dell REST API object.
:param volume: Cinder volume object.
:param scvolume: Dell Storage Center Volume object.
:param extra_specs: Extra specs if we have them otherwise gets them
from the volume.
:return: model_update'

def _create_replications(self, api, volume, scvolume, extra_specs=None):

    replication_driver_data = None
    if (not extra_specs):
        extra_specs = self._get_volume_extra_specs(volume)
    rspecs = self._get_replication_specs(extra_specs)
    if rspecs['enabled']:
        for backend in self.backends:
            targetdeviceid = backend['target_device_id']
            primaryqos = backend.get('qosnode', 'cinderqos')
            secondaryqos = backend.get('remoteqos', 'cinderqos')
            diskfolder = backend.get('diskfolder', None)
            obj = None
            if rspecs['live']:
                obj = api.create_live_volume(scvolume, targetdeviceid, rspecs['active'], rspecs['sync'], rspecs['autofailover'], primaryqos, secondaryqos)
            else:
                obj = api.create_replication(scvolume, targetdeviceid, primaryqos, rspecs['sync'], diskfolder, rspecs['active'])
            if (not obj):
                msg = (_('Replication    %(name)s    to    %(ssn)s    failed.') % {'name': volume['id'], 'ssn': targetdeviceid})
                raise exception.VolumeBackendAPIException(data=msg)
            if (not replication_driver_data):
                replication_driver_data = backend['target_device_id']
            else:
                replication_driver_data += ','
                replication_driver_data += backend['target_device_id']
    model_update = {}
    if replication_driver_data:
        model_update = {'replication_status': fields.ReplicationStatus.ENABLED, 'replication_driver_data': replication_driver_data}
    return model_update
