For a OAR setup with different set of nodes (i.e. different homogeneous clusters) in the resources, you might want to give different priorities to nodes, so that some nodes are used in priority compared to others.
For that purpose, you can use the scheduler_priority property of the nodes (setting it using the oarnodesetting command), which will be taken into account as specified per the SCHEDULER_RESOURCE_ORDER configuration setting in oar.conf.
Please mind also adding a 'cluster' property (oarproperty command and then oarnodesetting command) to identify cluster easly in oarsub commands, if one of the concern is to not have job mix nodes from old and new clusters.
e.g.: $ oarsub -p “cluster = 'my_brand_new_cluster'” …
which would be equivalent but maybe less cryptic than
$ oarsub -p “scheduler_priority = <value for the new cluster>'” …
The scheduler priority being a integer, it however allows for a -p switch such as “scheduler_priority >= <value>'”, let say if you have more than 3 clusters.