Hi Till, There are a couple of reasons to explain the independent reads:
1. they could be metadata reads issued by the HDF5 library 2. The HDF5 library is breaking collective access because it is not supported in your scenario. To check if 2 is the case and why the library is breaking collective, you could use the following function: https://www.hdfgroup.org/HDF5/doc/RM/RM_H5P.html#Property-GetMpioNoCollectiveCause Thanks, Mohamad From: Hdf-forum <[email protected]<mailto:[email protected]>> on behalf of Schumann Till <[email protected]<mailto:[email protected]>> Reply-To: hdf-forum <[email protected]<mailto:[email protected]>> Date: Tuesday, February 2, 2016 at 2:57 PM To: hdf-forum <[email protected]<mailto:[email protected]>> Cc: Kumbhar Pramod Shivaji <[email protected]<mailto:[email protected]>> Subject: [Hdf-forum] Parallel H5Read no collective Hi all, Im trying to read large amount of data via a H5Read collective operation from one dataset. Even though I passed the collective flag I see several MPI_File_read_at operation below (could see after an instrumentation with scorep) So I guess H5Read does not use collective IO. What I do: I access one large dataset with all processes. Each process reads a subset specified via hyperslabs (no overlaps). The dataset is a compound dataset containing: 1x Int and 5x float values. In memory I have a vector of struct objects: struct { a: int b: int <---- * c: int d float[5] <---- * } * only theses values should be assigned in memory. So I use H5Tcreate to create a compound memtype with the needed offsets. I use HDF5 1.8.15 I would welcome any hint. :) Thanks a lot! Till
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