If you have the option of expanding the C drive, that’s often the quickest way to get back up and running, but is generally only feasible in virtualized environments. If you’re reading this, that’s probably not an option for you. Quick ways to clear some space:
- Run Disk Cleanup, if you are on a Windows 2008 Server then you won’t have immediate access to disk cleanup but it can be added back using these instructions: https://technet.microsoft.com/en-us/library/ff630161(v=ws.10).aspx
- Move the swap file from the C drive to one of the other drives on the server (downside is this requires a reboot.
- Clear out the IIS logs in C:\Windows\system32\logfiles\w3svc
These files are safe to delete, however I would sort by date and delete all but the most recent file. This can clear several gigs on an Exchange server or other server with some IIS activity.
- Review the Folders on the C drive for junk thats been downloaded or saved
- Right click the C:\Users or C:\Documents and Settings and see how big it is, if it’s huge it could be worth while to drill into folders within profiles and see if there are any huge administrator user profiles, potentially with big downloads in them. Some applications like Symantec will bury gigantic multi-gig virus definitions in the All Users profile (research this issue if you have it for fixes from Symantec)
- Sort of last resort: Review C:\Windows and sort by data, move all the older ~NTUpdate folders from Windows Updates to a folder on say the D drive you create called “from C-Windows”. If you need to uninstall a Windows Update in the future you’ll need to move these folders back. Do this process very carefully, accidentally moving something out of C:\Windows that you shouldn’t have could have bad consequences.