OAR is a resource manager or (batch scheduler) for large clusters. In functionnalities, it's near of PBS, LSF, CCS and Condor. It's suitable for productive plateforms and research experiments.

By default IGGI OAR server use fping method to see if a node is Alive. It can report that a node is Alive, but in fact node is unavailable bu only respond to a ping. You can change this in /etc/oar.conf by using another method like the nmap one.

You can find more documentation about OAR here: OAR user guide. If this link doesn't work, you can see a snapshot doc: OAR user guide local