[MITgcm-support] MNC usage comment & more powerful version of gluemnc

[Martin Losch]

Mark,

I agree that mnc not overwriting existing files is a bit odd  
sometimes. But I think you should be fine with mnc_use_outdir=.false.  
if you just remove all grid.t???.nc files before restarting. The  
monitor files are not a problem as they follow the name convention  
monitor_$pkg.$niter0.t???.nc, niter0=0 if you start from rest and >0  
if you start from a pickup.
If you want to use mnc_use_outdir=.true., why don't you just link all  
files into a common directory, eg. "ln -s mnc*/*.nc ." before running  
gluemnc?

Further recommendation: Personally I have reverted to mdsio for  
pickup-files (mnc_write/read_pickup=.false.) in conjunction with  
useSingleCPUio = .true., (in data). This gives me one pickup file per  
package and not, say, 72, the seaice pkg (if you are using it)  
doesn't have netcdf pickup files anyhow. Also with this global pickup  
file you can easily change the number of tiles for the second  
segment, if you choose to do so. useSingleCPUio=.true. may also be  
faster on some machines where cpus access a global file system (I am  
told and that's also my experience).


Martin

On 22 Apr 2007, at 23:56, Mark Hadfield wrote:

> I'm trying to set up some reasonably large model runs with MNC  
> output. It's not clear to me how to arrange things for efficient  
> management of the output files and I'd appreciate some advice.
>
> It seems to be a fundamental design decision of the MNC package  
> that it will not overwrite existing netCDF files. This seems a  
> little odd to me, but there you go.
>
> OK, so I am running the model in two segments, the second being  
> started from the pickup files of the first. If I set MNC_USE_OUTDIR  
> to .FALSE. then the second run fails when trying to write  
> monitor_grid files, so I set MNC_USE_OUTDIR to .TRUE. and  
> MNC_OUTDIR_DATE to .FALSE. and I get my netCDF output in a bunch of  
> directories, one per processor per model run. These happen to be 72- 
> processor MPI runs, so the two model runs generate 144 directories.
>
> At the end I want to combine all the state files from these runs,  
> so I cd to the parent of the MNC output directories and type
>
> gluemnc mncout*/state*.nc
>
> This fails because gluemnc can't handle input file names with  
> directory separators in them. I have hacked gluemnc to avoid this  
> limitation. This hacking involved liberal use of the basename  
> command and I *think* it's working OK now.
>
> But this all seems awfully hard. Am I doing it wrong? Is there an  
> easier way of setting these things up?
>
> -- 
> Mark Hadfield          "Ka puwaha te tai nei, Hoea tahi tatou"
> m.hadfield at niwa.co.nz
> National Institute for Water and Atmospheric Research (NIWA)
>
>
>
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