[Mitgcm-support] Re: Global Files / MIT Model

[mitgcm-support at dev.mitgcm.org]

Hi John,

mitgcm.org had a disk problem last week but it back up now. I'll CC this there.

I agree with your assessment of the problem and we'll make those changes fairly
soon.

Thanks,

A.

John D Stark wrote:
> Hi Alistair,
> I sent the following to support at mitgcm.org, but it bounced ('Connection refused
> by mitgcm.org')  so, I'm sending it directly to you.  Is there a new support
> news group (it's no longer visible)? Thanks for the information you gave me
> earlier this month.
> 
> Cheers,
> John
> 
> Date: Fri, 11 Jan 2002 18:02:43 +0000 (GMT)
> From: John D Stark <jods at socnet.soc.soton.ac.uk>
> Subject: Reading / Writing Global files
> To: support at mitgcm.org
> MIME-Version: 1.0
> Content-MD5: CySUjCN5SYzpljLstJ0M6Q==
> 
> Hi,
> I spoke to Alistair earlier this week, who thought you may be interested in some
> of the coding I have been doing here in Southampton.  I hope this is useful for
> you.
> 
> Although global files are somewhat slower to write they are much easier to deal
> with, so I use them a lot.  However, with threads or MPI they just don't work.
> The main problem is that writing by multiple threads/ process to a single file
> is not safe, and the mdsio routines don't control this.
> 
> What is needed with global files is a large loop over processes within
> mdsio_writefield with a (MPI_)barrier at the bottom.  The loop / barrier should
> be dependent on whether globalfiles is true, which would minimise loss of speed
> with multifile writing.
> 
> I found that putting this in corrected problems I had with missing data in
> checkpoint files, and was also required for some netcdf file i/o I have added.
> 
> Note that adding a barrier in mdsio would mean that all higher level routines
> that enclose I/O in a begin_master / end_master section will cause a problem,
> notably write_state.
> 
> Cheers,
> John
> 
> ------------------------------------------
> John Stark
> Applications Programmer
> Southampton Oceanography Centre
> Tel. +44 (0)23 8059 6571
> e-mail jods at soc.soton.ac.uk
> ------------------------------------------