[mpich-discuss] single node mpiio

[Jaln]

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
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