Slowdown for large files?

[William Gropp]

I'm at the BG Scaling workshop in Germany, and Anshu is running the  
FLASH code with pnetCDF output.  She found that the output slowed to  
a crawl (a few dozen bytes/minute) after the file reached about 1/2  
GB (and that first 1/2 GB was written with reasonable speed).  This  
is from a multirack BlueGene to a GPFS file system.  I've asked her  
to try using POSIX write from a single BG processor to see if the  
GPFS installation slows down on large files.  Are there known issues  
we should know about?  Are there some tests that we could run,  
independent of FLASH, to test the pnetCDF output?  Thanks!

Bill