You may experience similar problems in version from Exchange 2010, here I have showcased an issue I faced in Exchange Server 2016 infrastructure.

You will see one or more of the following events/status on the server,

Explanation:

This issue can cause due to many factors, and most cases it can be mitigated by Solutions mentioned in the next section.

The reasons for this issues could be one or more of the following, but not limited to

1. Issues with “Microsoft Exchange Search” (MSExchangeFastSearch) Service
2. Issues with “Microsoft Exchange Search Host Controller” (HostControllerService) service.
3. Corrupt Content Index
4. Hard disk errors (read/write)

How to mitigate this issue, follow as suggested below!

Solution 1

Generally, this issue can be mitigated in one of the two list options below,

Option 1:

Consider you do not have any database copies with healthy Index State or the only server that host the database.

Stop the following services,

Delete the folder similar to the following from database path/location.

Start the Services in order,

The Exchange Server will initiate the process to rebuild the whole index. Depends on the data/size the process may take extended period of time. Wait for the process to finish, and in 90% of the case it will fix the issue.

Option 2:

If you have one “healthy” Content Index state database copy, reseed the database copy that has the unhealthy copy of content Index. In some cases when you add database copy in the DAG, the content index can go into unhealthy status (such as failed, unknown, failedandsuspended etc). To recover the content Index back to healthy, you can reseed the content index by running the “Update-MailboxDatabaseCopy” command with switch “-CatalogOnly”.

Update-MailboxDatabaseCopy LAB-DB03\EX16-01 –CatalogOnly

If you already tried this command, you may get the warning “Seeding cannot be requested for the same database copy until the failed request has been cleaned up by the server …”. Please say “y” to proceed with the reseed operations.

Verify the ContentIndexState after sometime, you will see a “healthy” state.

Solution 2

If the above steps did not go through fine, and if you receive errors similar to below even if all these services are healthy then it will be not an easy task to bring back your ContentIndexstate to healthy.

WARNING: Seeding of content index catalog for database 'LAB-DB03' failed. Please verify that the Microsoft Search (Exchange) and the Host Controller service for Exchange services are running and try the operation again. Error: An error occurred while processing a request on server 'EX16-03'. Error: An Exception was received during a FAST operation..

In some cases, there are disk errors but in my case the server was recovered from a unexpected failure which lead to run recovery steps on the database. Post the recovery the ContentIndexState was in healthy status in some database copies, but did not work quite fine in others.

Please note that the Content Index State only impact the end user experience, you are still allowed to mount the database on server where the Content Index State is not healthy. Hence the recommended approach is to create additional database and move the mailboxes gradually to get rid of the problematic database.

In my case, I also had the following event (Event ID 40025) logged on the server where this database was active.

Please share you comments or issues.

-Praveen