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Morten, After thinking more about the problem you uncovered with default chunk sizes in netCDF-4, I wondered why ordinary contiguous storage wasn't used for that case. I don't think there is any advantage to using chunked storage for variables that use only fixed-size dimensions and use no compression, checksums, or any other "filters" that require chunked storage. There is a large advantage to chunked storage if the data will be read in a different order than the order in which it was written, for example reading slices along the x or y dimension after writing slices along the z dimension. But there is also a price in performance if chunked storage is used instead of contiguous storage. For example, here are the times for writing the netCDF file in your example, with one 3D int variable dimensioned for 702 x 1201 x 1301: Using contiguous storage: 26.36user 28.57system 3:05.05elapsed 29%CPU (0avgtext+0avgdata 0maxresident)k 72inputs+16912048outputs (0major+109737minor)pagefaults 0swaps ls -l mwp-cont.nc -rw-r--r-- 1 russ ustaff 4387508754 Jan 24 06:55 mwp-cont.nc Using chunk sizes 351 x 601 x 651 46.10user 41.00system 3:53.36elapsed 37%CPU (0avgtext+0avgdata 0maxresident)k 5760inputs+17089216outputs (34major+1182343minor)pagefaults 0swaps ls -l mwp-cs.nc -rw-r--r-- 1 russ ustaff 4394540323 Jan 24 07:01 mwp-cs.nc Using the currently buggy default chunk sizes of 351 x 600 x 650 56.23user 75.91system 6:23.57elapsed 34%CPU (0avgtext+0avgdata 0maxresident)k 208496inputs+32052344outputs (34major+2515730minor)pagefaults 0swaps ls -l mwp-bug.nc -rw-r--r-- 1 russ ustaff 9856089091 Jan 24 07:08 mwp-bug.nc I think we should consider making the default storage layout contiguous instead of chunked for fixed-size variables when compression is not used, such as in your example. --Russ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu Ticket Details =================== Ticket ID: WWQ-664381 Department: Support netCDF Priority: High Status: Closed