A final note on accessing Large Files from IFS. I got a response from IBM support today that said while Large File support was enabled in V4R4M0, it was only for the POSIX functions [open(), read(), etc.] Other functions [fopen(), fread(), etc.] did not get Large File support until V5R1M0. If you back compile to V4R5M0 from V5R2 (I'd expect it at V5R1 as well) and use fopen() you are still limited by the 2GB limit. There is an error in a header file that instead of setting *IFS64IO back to *IFSIO changes it to *NOIFSIO instead.