public TSpaceQuotaResp getSpaceQuota() {
    TSpaceQuotaResp spaceQuotaResp = new TSpaceQuotaResp();
    if (!quotaInfo.getSpaceQuotaLimit().isEmpty()) {
      spaceQuotaResp.setSpaceQuota(quotaInfo.getSpaceQuotaLimit());
    }
    spaceQuotaResp.setStatus(RpcUtils.getStatus(TSStatusCode.SUCCESS_STATUS));
    return spaceQuotaResp;
  }
If the new quota is smaller than the quota already used, the setting fails.
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/ClusterQuotaManager.java