p-netcdf or netcdf4?

[michael]

On Tue, 2010-06-15 at 13:59 -0500, Rob Latham wrote:
> On Tue, Jun 15, 2010 at 07:51:21PM +0100, michael wrote:
> > All sounds good! And I keep aiming to upgrade my p-netcdf installation
> > sometime. 
> > 
> > However, I must hands up to some confusion: at a recent w/shop I was
> > informed netcdf-4 has its own parallel implementation and that I should
> > use that and forget p-netcdf (!). Can you clarify this for me?
> 
> I get asked this not-infrequently, so I wrote up a short response:
> 
> http://trac.mcs.anl.gov/projects/parallel-netcdf/wiki/PnetcdfAndNetcdf4
> 
> The relationship between the Netcdf4 developers and the
> parallel-netcdf developers is not nearly as contentious as that
> workshop would have you believe.  Both have their strengths.  I
> sympathise that more options can be more confusing.  
> 
> ==rob
> 

Rob, glad to see it's far from contentious. Just to clarify that page
(noting I'm not expect in the diffs from netcdf v3 to v4...):

 if I have netcdf v3 installed I can
   (a) replace some netcdf (v3) calls with p-netcdf calls, link to
p-netcdf, and get some parallelism (for an underlying parallel file sys)

 if I have netcdf v4 installed I can
   (a) amend my code from v3 to v4 then use the HDF5 "layer" to get some
parallelism
   (b) amend my code from v3 to v4, ensure I've p-netcdf installed, then
use the p-netcdf "layer" to get some parallelism

And I think Jim's just said (b) uses 10 times less memory than (a) but I
didn't pick up if there's much difference in I/O speed?

Many thanks, M
-- 
Dr. Michael K Bane
Senior Development Officer
RESEARCH COMPUTING SERVICES
Univ. of Manchester M13 9PL
http://www.rcs.manchester.ac.uk
http://twitter.com/mkbane_mcr