In Exchange 2010 after a database availability group (DAG) has been created it is necessary for administrators to add database copies to members.  This is generally accomplished using the add-mailboxdatabasecopy command.

When add-mailboxdatabasecopy is run, if the copy is successfully created an online seeding operation automatically occurs.  The online seeding operation that occurs utilizes the public / MAPI interface to initially seed the database.

It may be desired in certain instances to have the initial seeding operation occur over one of the private / replication networks defined for the DAG.  This is currently not possible since add-mailboxdatabasecopy does not implement the –Network parameter to specify an alternate network be utilized.

You can though work around this and achieve the initial seed over the private / replication network.  To do this:

Run add-mailboxdatabasecopy using the –seedingPostponed switch.  This will add the copy but not attempt the initial seeding operation.  It will also place replication in a suspended state.

Follow this up with update-mailboxdatabasecopy –Network and specify the private / replication DAG network.  This will allow the seeding operation to occur over the replication network.  Upon successful seed the replication instance will be automatically resumed.