# Changeset 5515 for trunk/DOC/TexFiles/Chapters/Chap_DIA.tex

Ignore:
Timestamp:
2015-06-30T13:34:00+02:00 (6 years ago)
Message:

Add some brief documentation of the CF compliance development.

File:
1 edited

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Unmodified
 r5107 The second functionality targets output performance when running in parallel (\key{mpp\_mpi}). Iomput provides the possibility to specify N dedicated I/O processes (in addition to the NEMO processes) to collect and write the outputs. With an appropriate choice of N by the user, the bottleneck associated with the writing of the output files can be greatly reduced. In version 3.6, the iom\_put interface depends on an external code called \href{https://forge.ipsl.jussieu.fr/ioserver/browser/XIOS/branchs/xios-1.0}{XIOS-1.0}. This new IO server can take advantage of the parallel I/O functionality of NetCDF4 to create a single output file and therefore to bypass the rebuilding phase. Note that writing in parallel into the same NetCDF files requires that your NetCDF4 library is linked to an HDF5 library that has been correctly compiled (i.e. with the configure option $--$enable-parallel). Note that the files created by iomput through XIOS are incompatible with NetCDF3. All post-processsing and visualization tools must therefore be compatible with NetCDF4 and not only NetCDF3. In version 3.6, the iom\_put interface depends on an external code called \href{https://forge.ipsl.jussieu.fr/ioserver/browser/XIOS/branchs/xios-1.0}{XIOS-1.0} (use of revision 618 or higher is required). This new IO server can take advantage of the parallel I/O functionality of NetCDF4 to create a single output file and therefore to bypass the rebuilding phase. Note that writing in parallel into the same NetCDF files requires that your NetCDF4 library is linked to an HDF5 library that has been correctly compiled (i.e. with the configure option $--$enable-parallel). Note that the files created by iomput through XIOS are incompatible with NetCDF3. All post-processsing and visualization tools must therefore be compatible with NetCDF4 and not only NetCDF3. Even if not using the parallel I/O functionality of NetCDF4, using N dedicated I/O servers, where N is typically much less than the number of NEMO processors, will reduce the number of output files created. This can greatly reduce the post-processing burden usually associated with using large numbers of NEMO processors. Note that for smaller configurations, the rebuilding phase can be avoided, even without a parallel-enabled NetCDF4 library, simply by employing only one dedicated I/O server. \subsection{XML reference tables} \label{IOM_xmlref} (1) Simple computation: directly define the computation when refering to the variable in the file definition. \end{longtable} \subsection{CF metadata standard compliance} Output from the XIOS-1.0 IO server is compliant with \href{http://cfconventions.org/Data/cf-conventions/cf-conventions-1.5/build/cf-conventions.html}{version 1.5} of the CF metadata standard. Therefore while a user may wish to add their own metadata to the output files (as demonstrated in example 4 of section \ref{IOM_xmlref}) the metadata should, for the most part, comply with the CF-1.5 standard. Some metadata that may significantly increase the file size (horizontal cell areas and vertices) are controlled by the namelist parameter \np{ln\_cfmeta} in the \ngn{namrun} namelist. This must be set to true if these metadata are to be included in the output files.