Using IBM Tivoli Network Manager with the most recent fixpack allows for the use of some great environmental variables for administering and controlling log and trace files.
The online documentation shows the setup or setting of the environmental variables, with references to any conflicts.
Online ITNM 3.9 Log rotation documentation
Take a look at some examples of questions from the field that are frequently seen.
setenv NDE_LOGFILE_MAXSIZE 1000000000