Yep, you’ve seen so many like this one, mostly they will suggest you to stop Exchange searching services, then delete the indexing folder (located inside the database folder) and then restart the searching services.

Well, that would work if you don’t have DAG.

Again, mostly you’ll find suggestions to use the update-mailboxdatabase with -catalogonly key

Yeah, that would work if any of the DAG members have a healthy catalog. Now what if all DAG members doesn’t have it?

You’ve two options, but both are risky and I have no responsibility what so ever happens to your data.

Option 1:

Remove one of the copies of the database from one DAG member

Delete the database folder copy from that member’s disk

Add the database copy again to the DAG member

Database index shows crawling for few hours, then healthy

Finally, you can use this new catalog to update other DAG members

Option 2 (have downtime):

Dismount all database copies on all DAG members

Shutdown Exchange searching services (two services) on all DAG members

Delete the catalog folder from all copies on all members

Restart Exchange searching services (two services) on all DAG members

All servers will start crawling

HTH