I ran into an issue when attempting to add a database copy for any mailbox databases in a new DAG. When I attempted it I kept receiving the following error every time, regardless of the source or destination server.
The seeding operation failed. Error: An error occurred while performing the seed operation. Error: An error occurred while processing a request on server ‘IC-OR-EXC-01’. Error: Database ‘b239a5e0-cbbf-46f2-9dde-1293d9c809bb’ was not active on source server ‘IC-OR-EXC-01’. [Database: Mailbox-IC-OR-EXC-01, Server: IC-OR-EXC-02.INDICIUM.CLOUD]
I worked out that due to the amount of Domain Controllers in my environment, replication hadn’t occurred yet so I just went for coffee and came back and all was good.
An alternative is to set the preferred domain controller to a Global Catalog DC residing in the same network using the following command:
Set-ADServerSettings -PreferredServer server.domain.com
Then go back to the Mailbox and click Resume: