In some cases, problems will arise with the index compiled by SharePoint 2010 that cannot be solved through normal means. For example, a particular item may have been deleted from the site but still appears in the index results despite numerous crawls. Or you might have unexplained errors appearing in the crawl log when you’re trying to index specific content. In cases like these, the solution may simply be to delete the index and start again with a fresh full crawl. You might also want to use this approach when you have a large amount of content referenced by your index and you need to perform a full crawl. A full crawl conducted after deleting the index often runs significantly faster than a full crawl against an existing index.
To delete the existing index and start a new index build, you first use the Index Reset command and then perform a full crawl.
WARNING Once the index has been reset, user search queries will no longer return results. It is a good idea to plan resetting the index for a weekend or a period of time when search will not be needed.
To reset the index, do the following:
1. From the Search Administration page, click Index Reset
2. On the Index Reset page, check the setting for the Deactivate Search Alerts During Reset option. This is checked by default so that search alerts are not fired on every item removal during the reset and every item addition during the full crawl. The alerts can be reactivated after the full crawl completes.
3. Click Reset Now.
4. Click OK.
5. Start a Full Crawl.