SUSDB.mdf is the WSUS database. There's a cleanup wizard in the WSUS Administration Console under Options. inetpub is for the IIS log files for WSUS. There was an issue with the original script responsible for deleting the old logfiles. The new script was automatically included in Windows Update.
Check this KB Article for the resolution:
http://support.microsoft.com/kb/2538579The log files grow when you leave the console open. If you close the SBS console when not in use, it will reduce the size.
Just as reference, mine is <100MB. So 30GB means your log files probably have never been cleared.
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