Before you migrate the Exchange Server 2010 mailbox databases, ensure that an active database and its copy databases use the same path in all servers. You have to install SnapManager on all member servers of the Database Availability Group (DAG) before migrating the mailbox databases.
If SnapManager is not installed on a member server of the DAG, all databases hosted by that member server, including both the active and passive databases, will not be migrated by SnapManager, and SnapManager will not be able to back up databases on that server.
Ensure that the database replication status is healthy before the migration.