[Beowulf] VASP on Clusters

Reuti reuti at staff.uni-marburg.de
Fri May 6 14:13:45 PDT 2005

Hi Dan,

are you using the same binary on both systems? Which compiler did you use? 
AFAIK, e.g. the Intel compiler output may use different operations, depending 
on the CPU where the created binary is running on.

If the results on the same type of machine is different between a serial run 
and a parallel run, I'd contact the author of the program. They have at least 
an eMail address for support. (But on two identical machines you got the same 
results for serial runs I hope.)

Cheers - Reuti

Quoting Daniel Majchrzak <dan at usf.edu>:

> We are having a problem running VASP on our clusters. (The old cluster
> is 48 nodes 1.8GHZ Atlons, 1GB RAM, GigE, and a slightly newer 12 node
> dual 2.6GHz Xeons, 2GB RAM, GigE) We have installed the program and run
> the benchmarks. (With some compilation adjustments on the old system to
> use smaller block sizes to eliminate some network receive buffer
> overruns.) Being a poor humble system administrator I don't pretend to
> understand the meaning of the output, but I'm assured that the results
> on both clusters were acceptable.  
> The problem is that when we run the program on larger jobs the results
> are inconsistent.  As I understand it, the older cluster will run small
> systems, but gives erroneous results on medium and large jobs.  The
> newer cluster gives good results on small and medium runs but fails on a
> large test case. (The results are different then those from a single
> processor job run on two different machines.)  I'm sorry for the
> somewhat vague description of small, medium, and large, but the experts
> tell me that there are so many different parameters to a VASP job that
> can increase the complexity of the run that it is nearly impossible to
> explain it to a mere mortal like myself.
> I'm doing some tests to see if the network buffer overruns have returned
> with these larger jobs, and if I can eliminate them by making the MPI
> block size even smaller but this reduces efficiency.)  I'm hoping a VASP
> expert on the list can point me to a solution, a set of minimal hardware
> necessary to avoid these problems, or telling me that it is impossible
> and that I should quit my job and just go get a beer.  I've looked for
> but not found a VASP users list, so I'm hoping someone on this list can
> help.
> Thanks,
> Dan
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