[Pvfs2-users] Problem, doubt with pvfs performance x nfs performance

[Robert Latham]

On Mon, Jan 29, 2007 at 05:54:44PM -0400, Luiz Mendes wrote:
> On all of my tests write files using MPI_File_write to a current NFS
> volume is faster than write to PVFS2..
> 
> For example, when i increase the number os threads, the bandwith
> decreases in both PVFS2 and NFS.
> 
> NFS in the examples have been 20 times faster than PVFS2.
> 
> Is it correct?
> 
> I am using a single computer. In 2 computers the results of PVFS2 is
> slower than using one. Am i doing something wrong to measure band?
> 
> I am not using too, pVFS2 kernell module, i am using it by MPI IO and MPI
> ROMIO.

Hi Luiz

What you describe makes sense: you are probably seeing NFS caching
behavior, while PVFS does not cache on clients.   If you want to
measure the effective bandwidh, you should either 

- time "open to close" for the two file systems, 
- or include the time for a call to MPI_File_sync after your last write 

==rob

-- 
Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Lab, IL USA                 B29D F333 664A 4280 315B