You can stop an update of a single content source. If you stop an update, you cannot continue the update.
When you stop an update, the update process stops only after it finishes processing the current document. The content index contains everything processed before you stopped the update, and on a single server configuration the changes appear in search results. However, in a server farm configuration, stopping an update of a content source prevents any updated documents from appearing in search results because propagation to the search servers does not occur. Propagating the index will cause the contents of the partially-updated index to be reflected in search results. For more information about propagating an index, see Propagating a Content Index.
Note In a server farm configuration, you cannot stop an update while it is propagating files to the search server.