One thing i have noticed with windows server is that IIS will keep on creating log files and won’t stop.
You should always delete IIS log files espicially on servers that OWA is being used on ALOT..
Log File locations:
Windows Server 2000/2003

Logfiles are here by default – %SystemDrive%\windows\system32\logfiles

Windows Server 2008

The default location for IIS Logfiles has been moved here - [...]