We came across an issues recently where one of our Exchange servers in a DAG started having the below errors appear in it’s Event Log.

Event ID 5301

Detected catalog corruption for database Database1

Event ID 123

At ‘9/20/2011 3:17:57 PM’ the Microsoft Exchange Information Store Database ‘Database1’ copy on this server experienced a corrupted search catalog. Consult the event log on the server for other “ExchangeStoreDb” and “MSExchange Search Indexer” events for more specific information about the failure. Reseeding the catalog is recommended via the ‘Update-MailboxDatabaseCopy’ task.

Basically the events were pointing to a corrupted catalog, so we simply fixed this by reseeding the catalog from another server that has a valid copy of the catlog via the following command

“Update-MailboxDatabaseCopy –Identity Database1Servername –CatalogOnly”

After running the above the errors disappeared Smile