[mpich-discuss] ROMIO hints start_iodevice, striping_unit, and striping_factor

[Rob Latham]

On Tue, Apr 21, 2009 at 12:20:34PM -0500, Wei-keng Liao wrote:
> I found the ROMIO hint start_iodevice appears in
> ad_pvfs/ad_pvfs_open.c, but is not defined in include/adioi.h. So,
> this hint is ignored by  ROMIO.  Can I suggest to add this to
> ADIOI_Hints_struct?

Hi Wei-keng.  

we can definitely add more things to ADIOI_Hints_struct.  Did you have
a particular use in mind for it?

> Two other hints, striping_unit and striping_factor, are defined but
> currently are only set by taking user's inputs. None of the ADIO
> drivers, except  PVFS-1, sets these hints by querying the file
> system. It would be nice to see  PVFS-2, Lustre, and GPFS (BGL) with
> this implemented, so users can query a  file's striping info through
> MPI_File_get_info(). In addition, file domain  alignment depends on
> the value striping_unit. It is important to detect this value
> automatically.
>
> One approach to add this functionality is to query the stripe info
> in ADIOI_xxx_Open by process fd->hints->ranklist[0] and broadcast it
> to the rest of processes (including cb_nodes and non-cb_nodes). The
> broadcast can be done in ADIO_Open() in ad_open.c

We recently (3 weeks ago) did something like this for ROMIO on
BlueGene.  I suppose the stat() interface is a lot more standard now
than 10 years ago.  We can probably move this out of blueGene and into
a generic form with little risk.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA