code: public long getUsedBytes() throws IOException {
      try (CloseableResource<BlockMasterClient> blockMasterClientResource =
          mContext.acquireBlockMasterClientResource()) {
        return blockMasterClientResource.get().getUsedBytes();
      }
    }
docs: Gets the used bytes of Alluxio's BlockStore.
  
  @return the used bytes of Alluxio's BlockStore