Drive space dwindling fast - can't tell why

I have a critical workstation here which I set up RAID 1 Mirrored.  Earlier this year both drives failed (one must have failed before the other one failed).  We had to rebuild the entire machine and replace the drives (Two High Speed SATAs  Western Digitals, 10000 RPM  so according to Dell the drives spend a lot of time working) .  

This morning were seeing error again on one drive.  The drive checked out OK using Dells Hard Disk Diagnostics tool  twice.  We ran chchDsk and it found an error (See attached).  Right now the system logs look clear.

But the bigger problem is the fact that I allocated 20GB to the C:\ drive initially which had about 8 or 9 GB free after the OS and core applications install.  Then suddenly (like overnight), There was only like 4GB free.   Today its down to 700MB.  I have looked everywhere for log files, cache use, temp files, Microsoft update files etc and cant tell what's using so much space.  

Could this be associated with a flaky Dell controller?  Can anyone help?
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I use a little utility called "Size Explorer Pro" in situations like this.. You can download a fully-functional time-limited trial.. Basically, you install it on your server, start the program and right-click/explore the system partition.. It looks like windows explorer, except files and folders at each level are sorted in descending size - including all sub folders etc.. Using this, you should know within minutes where all the space is going.. When you see a folder that's much bigger than it ought to be, open the folder and you'll see what files or folders inside are occupying all the space.. Like you, we only allocate a small system parition on a server - 8-10 GB and store data for all apps on other partitions..

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I don't think a controller error would cause the wrong amount of space to be reported - in the "olden days" you used to see controllers reporting more space than was physically available and sections of disk being overwritten by writes to other areas, but I don't think this is happening here, at least not if scandisk reports the disk integrity as being intact. See if you can determine where all the space is going first - it should be immediately obvious by adding up the file & folder sizes in the root of C: whether the file system is in fact intact
I use a utility called windirstat and it will scan your drive and show you how much space your files are taking up. Don't think the controller has anything to do with what you are seeing. I usually give more space to the C: drive as programs always store things there by default no matter what drive you install them to. So you always end up needing more space on C: than you planned.

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i would run Data Lifeguard on the drive just to make sure it not a drive issues..
To check to see what's eating up disk space, especially if it's overnight I suggest just using the built in windows search tool.  Use the advanced search features to search for files modified by date - since's it's like overnight then you could just search for any files modified or created within the last day or two. You can then sort by file size in explorer. You could also search for files greater than so many KB to find any large files that might be taking up space.  Make sure you choose the search option to search for hidden and system files too!
LTWadminAuthor Commented:
vertsyeux: The program you suggested worked GREAT.  Adobe Premiere was caching files out the wazoo even though the user was cleaning his cache.  Kudod to Chuck for suggesting the same approach...
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