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7.2.2 MNC Troubleshooting

7.2.2.1 Build Troubleshooting:

In order to build MITgcm with MNC enabled, the netCDF v3.x Fortran-77 (not Fortran-90) library must be available. This library is compposed of a single header file (called netcdf.inc) and a single library file (usually called libnetcdf.a) and it must be built with the same compiler (or a binary-compatible compiler) with compatible compiler options as the one used to build MITgcm.

For more details concerning the netCDF build and install process, please visit the netCDF home page at:

http://www.unidata.ucar.edu/packages/netcdf/
which includes an extensive list of known-good netCDF configurations for various platforms

7.2.2.2 Runtime Troubleshooting:

Please be aware of the following:

  • As a safety feature, the MNC package does not, by default, allow pre-existing files to be appended to or overwritten. This is in contrast to the older MDSIO package which will, without any warning, overwrite existing files. If MITgcm aborts with an error message about the inability to open or write to a netCDF file, please check first whether you are attempting to overwrite files from a previous run.

  • The constraints placed upon the ``unlimited'' (or ``record'') dimension inherent with NetCDF v3.x make it very inefficient to put variables written at potentially different intervals within the same file. For this reason, MNC output is split into groups of files which attempt to reflect the nature of their content.

  • On many systems, netCDF has practical file size limits on the order of 2-4GB (the maximium memory addressable with 32bit pointers or pointer differences) due to a lack of operating system, compiler, and/or library support. The latest revisions of netCDF v3.x have large file support and, on some operating systems, file sizes are only limited by available disk space.

  • There is an 80 character limit to the total length of all file names. This limit includes the directory (or path) since paths and file names are internally appended. Generally, file names will not exceed the limit and paths can usually be shortened using, for example, soft links.

  • MNC does not (yet) provide a mechanism for reading information from a single ``global'' file as can be done with the MDSIO package. This is in progress.


next up previous contents
Next: 7.2.3 MNC Internals Up: 7.2 NetCDF I/O: MNC Previous: 7.2.1 Using MNC   Contents
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