Volkhan runs the SLURM queuing system. The only volkhan-specific thing to know is that there is a partition called 'IB' containing compute nodes with Infiniband, a partition called 'NONIB' containing the ones without Infiniband, and a partition called 'CLUSTER' containing all the compute nodes. Only designated people may access 'IB' and 'CLUSTER'. Use the '-p' argument to salloc and sbatch to specify partitions. The system will simply pick one you can access if you don't specify which you want.
Because volkhan's nodes are a mixture of IB and non-IB we've configured the MPI libraries to try to use IB unless told not to. You will therefore get scary looking error messages about not being able to find a high performance transport when running MPI on non-IB nodes, but the jobs will still run.