Infiniband Upgrade
The GPC Infiniband (both QDR and DDR) are fully compatible in terms of hardware and software so no recompilation or different MPI flags will be required.
Job Submission
In terms of job submission, most things will remain the same for most users, however all jobs will now be infiniband based so the :ib: parameter used to ask for infiniband nodes will not be necessary anymore, however will still be accepted. By default a user's job will go to whichever network section best accommodates it, typically smaller jobs to the QDR and larger jobs to the DDR. However a user can override this by simply adding the flags "ddr" or "qdr" to the job resource request.
Two nodes anywhere
#PBS -l nodes=2:ppn=8,walltime=1:00:00
Two nodes using DDR
#PBS -l nodes=2:ddr:ppn=8,walltime=1:00:00
Two nodes using QDR
#PBS -l nodes=2:qdr:ppn=8,walltime=1:00:00
MPI Parameters
No special MPI parameters are required to run a job using Infiniband. It will be used by default so most users should just use the basic mpirun lines as outlined in GPC_MPI_Versions.
The NRAC allocations for the current year that were based on ethernet and infiniband will carry over, however the allocation will be on the full GPC, not just the subsection. So if you were allocated 500 hours on Infinibad your fairshare allocation will still be 500 hours, just 500 out or 30000, instead of 500 out of 7000. If you received two allocations, one on gigE and one on IB, they will simply be combined. This should benefit all users as the desegregation of the GPC provides a greater pool of nodes increasing the probability of your job to run.