I have a SharePoint 2007 front end server and the C: drive space started being consumed by something. I looked into it and some of the *.ci files from the C:\Program Files\Microsoft Office Servers\12.0\Data\Office Server\Applications\(guid)\Projects\Portal_Content\Indexer\CiFiles directory are huge, some ranging from from 200mb to 500mb. I think they are content index files.
Can I get rid of these files?
What are they tied to and why should I care about them?
You're correct, the .ci files are content index files. They store text from objects stored in your SharePoint farm to make them easily searchable. If you delete these .ci files, your search will break. Similarly, if you had a non-alphabetized dictionary and you tore out the index pages in the back that told you what page number a word could be found, you'd have to search every page in the book every time you wanted to find a word. You can tweak what gets indexed, but that's probably your only option. You could also move them to a drive that had more space.
http://technet.microsoft.com/en-us/library/dd255990(office.12).aspx