When installing OpenNMS on a clean Debian Jessie following the official documentation, jrrd2 is not installed. However, the setup process of OpenNMS complains about it missing:
"- Failed to load the optional jrrd2 library.

• This error is not fatal, since jrrd2 is only required for optional features.

• For more information, see http://www.opennms.org/index.php/jrrd2
  "
  The referred wiki page does not exist.