'Return the size[GB] of the specified volume.'

def manage_existing_get_size(self, existing_ref):

    ldev = _str2int(existing_ref.get('source-id'))
    if (ldev is None):
        msg = utils.output_log(MSG.INVALID_LDEV_FOR_MANAGE)
        raise exception.ManageExistingInvalidReference(existing_ref=existing_ref, reason=msg)
    return self.get_ldev_size_in_gigabyte(ldev, existing_ref)
