yes there is.<div><br></div><div>the problem in that case is that the IO and the solver use the same interconnect </div><div>where otherwise the solver uses infiniband and the IO the ethernet (this is the way most simple clusters are designed)</div>
<div>and there are a bunch of rather large mpi buffers being occupied by the IO.</div><div>i do not know how this will affect the performance as well.</div><div><br></div><div>Timo is right in that for large machines this in the only way to go but for smaller clusters i have my doubts.</div>
<div><br></div><div>cheers</div><div>Thomas</div><div><br><div class="gmail_quote">On Tue, Feb 28, 2012 at 4:44 PM, Wolfgang Bangerth <span dir="ltr"><<a href="mailto:bangerth@math.tamu.edu">bangerth@math.tamu.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im"><br>
> First: the solution to use MPI I/O and merge output files is the only<br>
> way to scale to bigger machines. You can not run with 10'000 cores and<br>
> write out 10'000 files per timestep.<br>
> Second: the merging of files is optional. It is a runtime parameter<br>
> you can set. You might want to generate one file per node (instead of<br>
> one file per core now) or you can leave it as it is today.<br>
<br>
</div>I think what Thomas meant to say is that somehow the data has to get<br>
from wherever you write it to the node that actually stores it. When you<br>
merge it using (synchronous) MPI I/O, you still have at least one node<br>
that has to wait till the writing is finished. This will take a long<br>
time no matter what you do (writing from each node to the central file<br>
system or writing via MPI I/O) and that the only way to avoid this is<br>
doing it in the background.<br>
<br>
Is there an asynchronous MPI I/O interface where you hand MPI the data<br>
and then go off doing something else while MPI decides what to do with<br>
the data?<br>
<br>
Best<br>
<div class="HOEnZb"><div class="h5"> W.<br>
<br>
------------------------------------------------------------------------<br>
Wolfgang Bangerth email: <a href="mailto:bangerth@math.tamu.edu">bangerth@math.tamu.edu</a><br>
www: <a href="http://www.math.tamu.edu/~bangerth/" target="_blank">http://www.math.tamu.edu/~bangerth/</a><br>
<br>
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