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Re: [Fwd: Re: netCDF file question]

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  • Subject: Re: [Fwd: Re: netCDF file question]
  • Date: Mon, 10 May 2004 09:42:47 -0600
> Subject: Re: netCDF file question
> Date: Fri, 7 May 2004 16:40:29 -0600 (MDT)
> From: <address@hidden>
> Organization: UCAR/Unidata
> To: address@hidden (John Caron)
> CC: address@hidden (WRF Help)

Hi Ms. Wei,

John Caron forwarded your question:

> We have recently run into problem of having WRF input and
> output files greater than 2 Gb for high-resolution model runs.
> Even though SCD has created a netCDF library for large files,
> we were not able to read the data back either in WRF model
> for input, nor in post-processors for output. 
> 
> From your understanding of the WRF data, should this be the
> case? I am trying to figure out if the problem is associated
> with WRF data, or with the lib out there on bluesky.

Were you able to successfully write large files?  If you can write
them successfully, then the library is OK and you should also be able
to read them.  If you can't write them successfully, what was the
error you got?

To successfully write large files with netCDF 3.5, you have to

 1.  Structure them correctly, see

      http://my.unidata.ucar.edu/content/software/netcdf/faq.html#lfs
     and
      
http://my.unidata.ucar.edu/content/software/netcdf/f90/documentation/f90-html-docs/guide9.html#2236524


 2.  Write them with a library built for large file support, which
     means at least having "-D_LARGE_FILES" included in the CFLAGS
     when the library was built.  It's my understanding this is the
     case for the library on bluesky.     

In addition, you also have to be writing to a file system configured
with large file support, but I can't imagine that the file system on
bluesky is not configured to support large files, so I doubt that is a
problem.

For your information, we will soon (this week) be releasing netCDF
3.6.0-beta, which will support 64-bit offsets and make it easier to
write very large netCDF files, without the restrictions caused by
32-bit offsets.  If it turns out the structure restrictions in
netcdf-3.5 don't let you write large files the way you want to, please
consider trying the new netcdf-3.6.0-beta for that purpose.

--Russ