iControl logging is controlled by the Local.Bigip.CORBA.LogLevel database key. A value of "DEBUG" produces verbose logging which is not intended for normal usage. A value of "INFO" produces logging at the user/request level. By default, the ITCM.log log file is rotated with the /etc/weekly script.
For more information about BIG-IP and it's operations please contact F5 Technical Support.
We had issues with the ITCM log filling up the volume it was on. I believe F5 set the log rotation to daily in 4.5 PTF 04? Still even without DEBUG turned on, if you're frequently getting node states or availability, the log can get very big very fast. Bulk calls for getting node states and availability would help tame this.
Also, starting with 4.5 PTF05, most messages currently seen today in ITCM.log will only be logged when the DEBUG database key mentioned above is set. This should help keep the log file size to the minimum.