I'm not sure about that. A record variable is *not* stored as a solid block. Instead each record stores the values of all record variables for just that record. A picture is here: http://www.unidata.ucar.edu/software/netcdf/docs/workshop/performance/FileFormat.html But you could still allocate space for a large number of records at the beginning of your program and gain some performance. For example, if you write a fake value into the 1000th record, all the other records will also be written and prefilled with fill values (assuming you haven't turned off prefilling), which will take some time at the beginning. But then the later addition of new records will be faster. --Russ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu Ticket Details =================== Ticket ID: GDB-514857 Department: Support netCDF Priority: Normal Status: Closed