code: @Override
  	protected synchronized void write(long offset, byte[] b) throws IOException {
  		if (byteBuffer != null) {
  			byteBuffer.position((int) offset);
  			byteBuffer.put(b);
  		} else {
  			throw new IOException("Write failed, file " + getPath() + " not mapped for I/O");
  		}
  	}
docs: Writes bytes to the underlying RRD file on the disk
  
  @param offset Starting file offset
  @param b	  Bytes to be written.