Recently on unmounting and remounting some exchange databases to stop 24/7 Maintence ( causing 8mb/s read traffic on our exchange EDB’s ) caused the search functionality to stop working

We had this before when the server , as we rebuilt the catalog files from Scratch ( Stop Microsoft Exchange Search Service, Delete the Catalog Folder for DB, Start Microsoft Exchange Search Service ) , however this puts heavy load on the exchange server as well as taking hours depending on the size of the DB ), and we wanted to get search returned ASAP

 We ran Troubleshoot-CI.ps1 which can be found in the Exchange\Scripts folder on the exchange server, which showed the server was deadlocked

 It logged events in the Microsoft-Exchange-Troubleshooters/Operational for the databases :

Detected indexing stall for database DatabaseName. Stall counter value 5059. Stall threshold value is 3600 seconds

We then Ran Troubleshoot-CI.ps1 -Action DetectAndResolve which restarted the Search Service ( Which we already did ) but it seemed to Disable it for a while which makes me think it did some other stuff!

Anyway search came back within 3 minutes of running , however it forced a reindex update across the rest of our Mailbox servers for some reason!