Roy, A little more information on this. According to a presentation given in November at the HDF/HDF-EOS workshop, groups have overhead for a B-tree used to manage the objects in each group. This overhead is fairly significant. An example given is an HDF5 file with 11,600 groups that used to require 20 MB in HDF5 version 1.6 but now requires only 12 MB in HDF5 version 1.8. That works out to about 1000 bytes/group overhead, which may discourage use of lots of small groups ... --Russ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu Ticket Details =================== Ticket ID: QEA-741463 Department: Support netCDF Priority: Normal Status: Closed