Environment
Notification Server 6.0 SP3
Any size C drive (the drive being filled will usually be the same drive the OS is installed on).
Cause
There may be many causes for your C drive to fill up, but in this case the administrator had only installed the operating system and very few applications.
Upon further inspection, I discovered that the folder taking up the most space was the C:\Windows\System32\Logs\W3SVC1 folder (the number at the end may differ, W3SVC followed by the number of the Web site it's designated for. In this example it was the default Web site). The log files were getting as large as 600MB any given day. The log files had not been purged/cleared out in years.
Resolution
It's good practice to periodically go through your log files that are not automatically purged and remove (or move) old ones that you will no longer need. You might also want to consider making some adjustments to your logging settings to take less information, but this will depend on your company's needs.
The most common options are:
If you decide to not log anything (not recommended), you can follow steps 2a through 2c, and then uncheck the Enable logging check box.