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-   -   Using several nodes in a simulation (OpenFOAM) (https://www.cfd-online.com/Forums/openfoam/222618-using-several-nodes-simulation-openfoam.html)

Didu December 2, 2019 05:35

Using several nodes in a simulation (OpenFOAM)
 
Dear all,
I'm quite new in using OpenFOAM in a cluster, using only one node is a breeze...
the problem starts when I need to use more than one node...
I'm using the command 'mpirun --host node1,node2 -np 48 rhoSimpleFoam -parallel' and I get the following info/error

There are not enough slots available in the system to satisfy the 48
slots that were requested by the application:

rhoSimpleFoam

Either request fewer slots for your application, or make more slots
available for use.

A "slot" is the Open MPI term for an allocatable unit where we can
launch a process. The number of slots available are defined by the
environment in which Open MPI processes are run:

1. Hostfile, via "slots=N" clauses (N defaults to number of
processor cores if not provided)
2. The --host command line parameter, via a ":N" suffix on the
hostname (N defaults to 1 if not provided)
3. Resource manager (e.g., SLURM, PBS/Torque, LSF, etc.)
4. If none of a hostfile, the --host command line parameter, or an
RM is present, Open MPI defaults to the number of processor cores

In all the above cases, if you want Open MPI to default to the number
of hardware threads instead of the number of processor cores, use the
--use-hwthread-cpus option.

Alternatively, you can use the --oversubscribe option to ignore the
number of available slots when deciding the number of processes to
launch.

I'm doing something wrong, please help...
OpenFOAM - v1906


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