The netCDF output format provides a self-describing output file which is portable across machines. It is also recognized by many graphics and post-processing utilities. These are important and very useful features and are the reasons a netCDF option has been included in POP. However, there are two disadvantages to using this format.
The most serious disadvantage with netCDF format is that netCDF does not currently permit parallel I/O; all netCDF operations are funneled through a single processor. For high resolution simulations, this can present a serious performance bottleneck as the model attempts to pass several Gbytes through a single processor. If netCDF output is desired and is proving to be too slow, the user should switch to binary format and convert the binary files off-line to netCDF.
Currently, the data portion of a netCDF file utilizes IEEE binary format. For portability, if a machine does not use IEEE format for its native binary format, netCDF will be performing a conversion (hidden to the user) to this format. In such a case, loss of precision during this conversion will occur and exact restart can not be guaranteed. To avoid this, binary format should typically be chosen for all restart files.