It should be noted that no UNICOS platform has been available at Unidata for netCDF testing for some years. The following information is left here for historical reasons.
As was mentioned in the previous section, it is possible to replace the I/O layer in order to increase I/O efficiency. This has been done for UNICOS, the operating system of Cray computers similar to the Cray Y-MP.
Additionally, it is possible for the user to obtain even greater I/O efficiency through appropriate setting of the NETCDF_FFIOSPEC environment variable. This variable specifies the Flexible File I/O buffers for netCDF I/O when executing under the UNICOS operating system (the variable is ignored on other operating systems). An appropriate specification can greatly increase the efficiency of netCDF I/O–to the extent that it can surpass default FORTRAN binary I/O. Possible specifications include the following:
bufa:336:2
cache:256:8
cachea:256:8:2
cachea:8:256:0
cache:8:256,cachea.sds:1024:4:1
All of the options/configurations supported in CRI's FFIO library are available through this mechanism. We recommend that you look at CRI's I/O optimization guide for information on using FFIO to its fullest. This mechanism is also compatible with CRI's EIE I/O library.
Tuning the NETCDF_FFIOSPEC variable to a program's I/O pattern can dramatically improve performance. Speedups of two orders of magnitude have been seen.