[aspect-devel] Writing output in parallel

[Thomas Geenen]

yes there is.

the problem in that case is that the IO and the solver use the same
interconnect
where otherwise the solver uses infiniband and the IO the ethernet (this is
the way most simple clusters are designed)
and there are a bunch of rather large mpi buffers being occupied by the IO.
i do not know how this will affect the performance as well.

Timo is right in that for large machines this in the only way to go but for
smaller clusters i have my doubts.

cheers
Thomas

On Tue, Feb 28, 2012 at 4:44 PM, Wolfgang Bangerth
<bangerth at math.tamu.edu>wrote:

>
> > First: the solution to use MPI I/O and merge output files is the only
> > way to scale to bigger machines. You can not run with 10'000 cores and
> > write out 10'000 files per timestep.
> > Second: the merging of files is optional. It is a runtime parameter
> > you can set. You might want to generate one file per node (instead of
> > one file per core now) or you can leave it as it is today.
>
> I think what Thomas meant to say is that somehow the data has to get
> from wherever you write it to the node that actually stores it. When you
> merge it using (synchronous) MPI I/O, you still have at least one node
> that has to wait till the writing is finished. This will take a long
> time no matter what you do (writing from each node to the central file
> system or writing via MPI I/O) and that the only way to avoid this is
> doing it in the background.
>
> Is there an asynchronous MPI I/O interface where you hand MPI the data
> and then go off doing something else while MPI decides what to do with
> the data?
>
> Best
>   W.
>
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                 www: http://www.math.tamu.edu/~bangerth/
>
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