Re: [Libmesh-users] Parallel mesh and mesh/solution IO

[Lorenzo B. <bot...@gm...>]

Thanks for the hints.
Just a question... It seems that you prefer the Nemesis format  
compared to the native xdr xda, is there any reason for that?
I don't know if I will have time to do it in the near future because  
the end of my PhD is approaching very fast.
Anyway I think that parallel IO for mesh and solution is crucial to  
run parallel (>100 processes) computations, and of course ghosted  
vector is crucial too (thanks Tim).

Lorenzo

Il giorno 21/ott/2009, alle ore 17.47, Derek Gaston ha scritto:

> 1) In certain circumstances.... but probably not huge.
>
> 2) Yes
>
> 3) You can read and write parallel xda/r files.... although I  
> haven't done it myself.  BUT... it looks like that is only possible  
> when writing the entire equation system not just the mesh.  I don't  
> know if there is a way around that.  Maybe Ben will chime in.
>
> Although:
>
> 4) Currently libMesh does support _reading_ of Nemesis meshes.   
> These are Exodus meshes that have been _pre_ decomposed so that each  
> piece of the mesh resides in a different file and each processor  
> only reads it's part of the mesh.  I can verify that that does work  
> with ParallelMesh (although a few of the more advanced things in the  
> Exodus reader aren't supported yet).
>
> However... the _writing_ of Nemesis meshes / solutions isn't  
> supported yet... so to get output you still have to do the old  
> serialization.  I hope to change that in the not too distant  
> future... but it continues to slip down my TODO list.
>
> If you are interested in helping out with getting Nemesis writing  
> going you can get the documentation here: http://sourceforge.net/projects/exodusii/files/ 
>   .  Once we have Nemesis read / write capability we will have a  
> complete end-to-end parallel capability.
>
> Derek
>
> On Mon, Oct 19, 2009 at 9:30 AM, Lorenzo Botti  
> <bot...@gm...> wrote:
> I'm planning to perform a lot of parallel runs (without AMR) on a big
> cluster and I would like to know a couple of details about the  
> parallel mesh
> implementation.
> 1) Is it faster than serial mesh?
> 2) Does it use less memory per process?
>
> 3) Is it possible to read and/or write parallel .xdr/.xda data files?
> I'm curious about the possibility of making a mesh partitioning and  
> write
> the single partition files so that every process involved in a  
> parallel
> computation loads just one portion of the mesh. Does this approach  
> gives
> some benefits?
>
> 4) Have you planned to introduce some parallel solution output  
> format? I
> think that having to serialize the solution is quite an expensive  
> operation
> for unsteady computations.
>
> Thanks a lot.
> Lorenzo
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