[gpaw-users] HDF5 and parallel calculation support

[Jussi Enkovaara]

On 2013-01-22 21:21, Gaël DONVAL wrote:
> Hi everyone,
>
> I'm about to install gpaw on our computer cluster.
>

>
> The question is, is there any support for the HDF5 format in gpaw
> without parallel compilation of the HDF5 library? I tried to compile
> HDF5 with parallel support but since the FS we used is not parallel yet,
> we don't even have the MPI/IO extension compiled in OpenMPI.

Hi,
the short answer is that currently one cannot use parallel GPAW with
serial HDF5 (it is, however, possible to use serial GPAW with serial
HDF5).

When using .gpw files, all the data is collected to single process which
does then the I/O, and while in principle similar thing could be done
with HDF5, I do not think it is worth of implementing.

There are only two MPI I/O related HDF5 functions used in GPAW, and even 
tough the one of them (which enables collective I/O) can be
disabled easily, the other one used for opening the file for parallel
access is really required. At least very brief test on our Cray system
showed that file write does not work correctly (with more than single
CPU core) if file is not opened for parallel access.

Best regards,
Jussi