Will I experience any downtime during reindexing while migrating my applications to Acquia Search powered by SearchStax?

You will experience a downtime when you replace the indexes and click the reindex button. To prevent the downtime, use the migration module that is available as a sub-module on drupal.org. The module creates a copy of the index and allows you to reindex the data to the copy without affecting live traffic. After the system indexes the data, click the migrate button to switch views to direct users to the new search index and achieve zero downtime.