Hi, I'm running hdft with mpiio on a single compute node (32 cores), 10 OSTs, the file system is lustre v2.5. I submit the job with 3 processes, they are writing to a shared file, which is about 3GBs, and each process writes 1/3 of the file, for example, The array is a 4D double array, 3*32*1024*128, then each process writes 32*1024*128 to the file, which is contiguous. I observed some wired performance number, I tried both independent I/O and collective IO. In the case of independent I/O, each rank seems to block each other and finish writing one after another. But in collective I/O, all three ranks reports same I/O cost, I think this is because there is only one aggregator. My question is, in the case of independent I/O, are the I/Os blocking when accessing the file? If not blocking, can I expect linear speedup on a single node by increasing number of processes? Best, Jialin Lawrence Berkeley Lab _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss