'Return size of an existing VMAX volume to manage_existing.
:param self: reference to class
:param volume: the volume object including the volume_type_id
:param external_ref: reference to the existing volume
:returns: size of the volume in GB'

def manage_existing_get_size(self, volume, external_ref):

    return self.common.manage_existing_get_size(volume, external_ref)
