Why is there delay in starting parallel sim?
 

I am trying to run drivaerFastback tutorial in parallel, with background option using command below



mpirun -np 4 simpleFoam -parallel > log &


It seems like it is in queue as cmd show [1]64126


However, it doesn't get updated for 20 minutes and log file is still empty


I've tried same sim few hours ago on foreground without " > log & " , and it started more than 30 minutes passed. (IDK how accurate delay was bc i was tired of waiting and just went out for lunch, and it was running when i returned)


So I first thought it may be problem of # of mesh, and it may be because just it takes too long to allocate data to each processor and tried with very simple cavity case


It still spent more than 10 minutes with nothing happening, and I just aborted it.


But it just worked 1 second to complete simulation without parallel option, by just typing single word 'icoFoam'


Why does it take so long for parallel mpi sim to start?