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Hi All, I have implemented access to the netCDF4 chunking features in NCO. The "all or nothing" approach---chunking all the variables or none--- usually works as expected. However, "moderately chunked" approaches--- where, say, only the 3D variables are chunked, or only the variables containing a certain dimension---often fail in the HDF library (error code -101 = "HDF error"). Also, unchunking a completely chunked dataset fails. As I understand it, the chunking of one variable is completely independent of the chunking of the rest of the variables, i.e., netCDF4 imposes no special restrictions on chunking (or not) coordinate variables, record variables, etc. To me, this indenpendence means that if I chunk one variable that contains a certain dimension, "longitude" say, then I do not have to chunk all the other variables that contain "longitude". My understanding is that I can chunk (or not) any variables I like as long as each dimension's chunk size is <= the dimension size. Are there any chunking constraints/limitations present in the HDF layer that might cause the symptoms I encounter? As important, I do (sometimes) call nc_def_var_chunking() multiple times for the same variable before an nc_enddef(). I assume this is OK and that each variable will be written with the parameters set for it in the last nc_def_var_chunking() call before nc_enddef(). Thanks, Charlie -- Charlie Zender, Department of Earth System Science University of California, Irvine (949) 824-2987 :)