In Exchange 2010 the out of box behavior for a database availability group (DAG) is to utilize native replication based on log shipping. Some customers choose to leverage solutions provided by vendors that support the third party replication API thereby replacing the inbox replication mechanism.
Recently I worked with a customer leveraging the third party replication API and had a move mailbox performance issue. Overall move mailboxes were under performing what was expected. After investigation we were able to determine that the databases hosted on the DAG had the default DataMoveReplicationConstraint property specified. By default this property is set to secondCopy. The purpose of this property is to allow the mailbox replication service on a client access server to throttle move mailbox based on the replication status of the target database. In the case of the third party replication API it is not necessary to set this constraint. By default all vendors leveraging the third party replication API must support synchronous replication, therefore writes are automatically throttled based on the ability to replicate synchronously thereby making it not necessary to utilize the DataMoveReplicationConstraint.
When using the third party replication API it is recommended to disable the DataMoveReplicationConstraint using the set-mailboxdatabase commandlet to a value of NONE.
Corrected mis-spelling of the DataMoveReplicationConstraint