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