[netCDF #VMY-113616]: possible variable size limit/error in netCDF 3.6.2

Hi Wes,

If you read the netCDF FAQ section on Large File Support:

http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#Large%20File%20Support

(or the section of the Users Guide on this subject) it notes that there are 
still some limits to netCDF variable sizes, even when using 64-bit offsets:

Have all netCDF size limits been eliminated?

No, there are still some limits on sizes of netCDF objects, even with the new  
64-bit offset format. Each fixed-size variable and the data for one record's 
worth of a record variable are limited in size to a little less that 4 GiB, 
which is twice the size limit in versions earlier than netCDF 3.6.

Why are variables still limited in size?

While most platforms support a 64-bit file offset, many platforms only support 
a 32-bit size for allocated memory blocks, array sizes, and memory pointers. In 
C developer's jargon, these platforms have a 64-bit off_t type for file 
offsets, but a 32-bit size_t type for size of arrays. Changing netCDF to assume 
a 64-bit size_t would restrict netCDF's use to 64-bit platforms.

This is the limit you are running into, trying to create a non-record variable 
with 2^30 4-byte values, which just exceeds the 4 GiB limit on the size of a 
variable.  Using an unlimited dimension should permit much larger variables, so 
long as a record's worth of data for each record variable does not exceed 
2^32-4 bytes.  For details, see:

http://www.unidata.ucar.edu/software/netcdf/docs/netcdf/NetCDF-64-bit-Offset-Format-Limitations.html

If you still have questions about this or think there is a bug, please let us 
know.  We think these limits are all tested when you run "make check" if you 
have run te configure script with the --enable-large-file-tests option and 
--with-temp-large=<directory> to specify a directory where large files will be 
written, if large files tests are run.

--Russ


Russ Rew                                         UCAR Unidata Program
address@hidden                     http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: VMY-113616
Department: Support netCDF
Priority: Normal
Status: Closed