RE: [bgl-discuss] Blue Gene slow I/O

["Sindhi, Abdul Waris" <abdul.sindhi@xxxxxxxxxx>]

Yes, each process writes to a separate file, and all the
processors do perform I/O around the same time. Each process 
is writing contiguous blocks to its own file.

Lastly no, we are not using MPI-IO.

Thanks,
Waris

-----Original Message-----
From: William Gropp [mailto:gropp@xxxxxxxxxxx] 
Sent: Monday, December 04, 2006 12:55 PM
To: Sindhi, Abdul Waris
Cc: discuss@xxxxxxxxxxxxxxx
Subject: Re: [bgl-discuss] Blue Gene slow I/O

Could you give us a few more details?  Is each process writing to a  
separate file, with all processes writing at about the same time?   
Are they writing contiguous blocks to the same file, with the blocks  
aligned on block boundaries?  Are they writing multiple segments to  
the same file, with each process contributing some set of segments?

Do you use MPI-IO?  If so, which MPI-IO routines do you use?  If not,  
would you be willing to consider using MPI-IO?

Thanks!
Bill

On Dec 4, 2006, at 10:13 AM, Sindhi, Abdul Waris wrote:

> We are running a CFD application on the Blue Gene that performs  
> sequential
> I/O on all the processors at around the same time. The case we  
> currently run
> is out of user homedir. We are currently running a 40 processor  
> breakup, and
>
> the read/writes are to a file sized around ~20MB.
>
> The read/write performance looks pathologically slow at around  
> 20-30 times
> slower when compared to normal runs. We are wondering if anyone  
> else has
> run into similar issues with slow I/O on the Blue Gene ?
>
> Thanks,
> A. Waris Sindhi
> High Performance Technical Computing
> Pratt & Whitney, UTC
> (860)-565-8486
>
> - --------------------------------------------------------------------
> To add or remove yourself from this mailing list, use the 'notifyme'
> command on any BGL machine. To remove: notifyme -n, to add:  
> notifyme -y.
>

- --------------------------------------------------------------------
To add or remove yourself from this mailing list, use the 'notifyme'
command on any BGL machine. To remove: notifyme -n, to add: notifyme -y.