What is a crawl database?
In Search Server 2010, a crawl database contains data that are interrelated with the location of content sources, crawl schedules, and other information specific to crawl operations for a specific Search service application. The database load can be distributed by adding crawl databases to different computers that are running SQL Server. Crawl databases are associated with crawl components and can be associated with specific hosts by creating host distribution rules.
What is a crawl component?
In Search Server 2010, a crawl component is used to process crawls of content sources and propagates the resulting index files to query components. It adds information about the location and crawl schedule of content sources to their associated crawl databases. Crawl components are associated with a single Search service application and can be added to different farm servers for distributing the crawl Load.