Let see how to rebuild and Content Index on Exchange 2013/2016 if the content index of the primary database went to a bad shape.
Note : This process takes more I/O on your disk . and increases the load on the server. if you have multiple databases on the same disk/server. Consider doing one by one.
If the Content index of the DAG copy failed you can run
Update-MailboxDatabaseCopy "DBname\Servername" –CatalogOnly
If the Content index of the primary DB failed
Get-MailboxDatabaseCopyStatus -Server EXCH2016A | fl
SinglePageRestore : 0
ContentIndexState : FailedAndSuspended
ContentIndexErrorMessage : The content index is corrupted.
ContentIndexErrorCode : 19
Stop below Exchange Services –
Microsoft Exchange Search – MSExchangeFastSearch
Microsoft Exchange Search Host Controller – HostControllerService
Go to the affected database location – Move the Catalog folder to a different location –
Start the above services back.
Content Index will kick off (This process takes time)– going to unknown –> Crawling –> Healthy.