Of course, a much simpler way to do this is to create the file using 
MPI_COMM_SELF, create the data sets independently as you did since collective 
on comm_self is well, independent, and close the file. 
Then you can actually open the file again using comm_world, open the dataset 
for each process (H5Dopen is not collective), then access the dataset for each 
process independently as you were doing.

Mohamad


On Dec 11, 2012, at 10:19 PM, Mohamad Chaarawi <[email protected]> wrote:

> 
> 
> On Dec 11, 2012, at 9:33 PM, Suman Vajjala <[email protected]> wrote:
> 
>> Hi,
>> 
>>  I thank you for the replies. The problem is that for creating a dataset 
>> using H5Dcreate every processor has to know that dataset's size. Is there a 
>> way of of doing it without the processors knowing the data size.
> 
> If the dataset size if based on the process rank, then you can just calculate 
> that at each process then call H5Dcreate collectively on all processes for 
> each dataset. If you can't calculate that size at each process, you can use 
> MPI_Allgather to distribute the size for each process to all other processes 
> then you would be able to call the H5Dcreate n times.
> 
> This is a limitation currently in the HDF5 standard that we plan to relax in 
> the future. But this work is still in the prototyping stage. Ping me early 
> January and might have a beta version that you might be able to use.
> 
> Mohamad
> 
>> 
>> Regards
>> Suman 
>> 
>> On Wed, Dec 12, 2012 at 8:58 AM, Elena Pourmal <[email protected]> wrote:
>>> reate ia
>> 
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