
Explanation:
Box 1: ..with CHECKSUM option
Azure Database Migration Service does not initiate any backups, and instead uses existing backups, which you may already have as part of your disaster recovery plan, for the migration. Be sure that you take backups using the WITH CHECKSUM option.
Box 2: An SMB share
For online migrations from SQL Server to SQL Managed Instance using Azure Database Migration Service, you must provide the full database backup and subsequent log backups in the SMB network share that the service can use to migrate your databases.
Reference:
https://docs.microsoft.com/en-us/azure/dms/tutorial-sql-server-managed-instance-online