One more question about hdf5 parallel data set creation: here<http://www.hdfgroup.org/hdf5-quest.html#par-nodata>two alternatives are presenting for writing data from a subset of MPI ranks. I will be writting to a lustre filesystem, and and was wondering about the performance differences between the two techniques. I have ordered data in a 3D array, and the domain decomposition is done over the 2nd and 3rd indices (Fortran code). So each MPI rank has a 3d array. The domain is decomposed, and the processors layed out, as a 2D grid. I want to write 2D planar slices of data out with high frequency. If the slice is taken as j=const or k=const (where j and k are the 2nd and 3rd indices respectively, the indeces which the separate subdomains) then only a relatively small (compared to the total #) but still O(10-100) MPI ranks need to write data. I would say in general less than 50% but more than 10% of the MPI ranks will be involved in this write. Should I do it as a collective write where I guess there is some over-head as the MPI ranks are cycled through in a predetermined order, or should I hammer the lustrefs with uncoordinated individual writes, concurrently? Any insight here is appreciated.
Many thanks, Izaak Beekman =================================== (301)244-9367 UMD-CP Visiting Graduate Student Aerospace Engineering [email protected] [email protected]
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