code: static MD5Hash downloadImageToStorage(String fsName, long imageTxId,
        FSImage dstImage, boolean needDigest, boolean disableThrottle)
        throws IOException {
  
      String fileid = GetImageServlet.getParamStringForImage(
          imageTxId, dstImage.storage, disableThrottle);
      
      List<OutputStream> outputStreams = dstImage.getCheckpointImageOutputStreams(imageTxId);
      
      if (outputStreams.size() == 0) {
        throw new IOException("No targets in destination storage!");
      }
      
      MD5Hash hash = getFileClient(fsName, fileid, outputStreams, dstImage.storage, needDigest);
      LOG.info("Downloaded image files for txid: " + imageTxId);
      return hash;
    }
docs: Download image to local storage.
  Throttling can be disabled.