> On Oct 23, 2014, at 4:25 AM, Heiko Klein <Heiko.Klein@xxxxxx> wrote:
> when chunking files with unlimited dimension, the unlimited dimension must be
> given explicitly in nccopy, and will usually be set to one.
Careful with"usually"....
> In a file with time as unlimited dimension, and X and Y as dimensions, it is
> currently required to use
>
> $ nccopy -k 4 -c "time/1,X/100,Y/100" in.nc out.nc
>
> When running without time, it does not work:
>
> $ nccopy -k 4 -c "X/100,Y/100" in.nc out.nc
> NetCDF: Invalid argument
> Location: file nccopy.c; line 637
>
>
> Only for unlimited dimensions, one needs to give the dimension explicitly,
> for all other dimensions a useful default (full dim-size) is used. I think a
> useful default for unlimited dimensions is 1.
It does make sense to have a useful default, yes. And I thought the
netcdf lib itself does have defaults, so this may be a bug only in
nccopy.
And, indeed the lib used to default to 1 for unlimited dimensions.
However, 1 is a very bad default if you have a 1-d array or the other
dimensions are small. I think this had been fixed in the lib itself,
but we do want to make sure 1 isn't used as a default always.
Actually, a better way to think about is that the total size of the
chunks should not be too small. Even your 1x100x100 example above is
pretty small on modern hardware.
-Chris
>
>
> Heiko
>
>
>
> --
> Dr. Heiko Klein Tel. + 47 22 96 32 58
> Development Section / IT Department Fax. + 47 22 69 63 55
> Norwegian Meteorological Institute http://www.met.no
> P.O. Box 43 Blindern 0313 Oslo NORWAY
>
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