Hi Dennis:
I asked about this also awhile back. The key question to my mind is how the
virtual dataset works in HDF5. Perhaps the interface is such is that it is
transparent to higher level calls, much like when you create virtual datasets
in TDS. In that case, the calls would be to as if there was one file.
-Roy
> On Jul 13, 2016, at 2:09 PM, dmh@xxxxxxxx wrote:
>
> To this point in time, it has been an implicit assumption
> that a netcdf dataset encompasses a single file. This functionality
> effectively challenges that assumption. So, I would solicit
> community input on this. What problems are created if a netcdf
> dataset now requires multiple files?
>
> =Dennis Heimmbigner
> Unidata
>
>
> On 7/13/2016 5:09 AM, Eugen Betke wrote:
>> Dear NetCDF-Group,
>>
>> we have been working on NetCDF external link functionality. This allows
>> NetCDF applications to create dimension variables which values are
>> stored in an external file. Therefore, it uses the HDF5 virtual dataset
>> (VDS) functionality. This is useful for, e.g., climate applications that
>> rely on a variable per file and timestep configuration. The idea is to
>> store the grid in a separate file and link our data to this grid. We
>> already have our first working version. You find the patch and the
>> examples on our page:
>>
>> http://wr.informatik.uni-hamburg.de/research/projects/bullio/netcdf_external_links/start
>>
>>
>> Under the hood it uses HDF5 virtual datasets. VDS has the advantage of
>> being compatible to the functions that are supported by oridinary
>> datasets. Therefore, files containing VDS should be supported by the
>> most software.
>>
>> There is a minor issue related to HDF5, the call H5F_try_close function
>> fails, when ncdump trys to read data from an external dimension. So far
>> we found a workaround, but we will fix this issue.
>>
>> It would be great if external link functionality could be supported by
>> netCDF at some timepoint. We would like to improve our patch and for
>> that reason we need your feedback. If you have some idea to the issue
>> above, we would be grateful for each hint.
>>
>> Regards,
>> Eugen
>>
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NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
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