Remove Exchange 2010 Archive Database from Provisioning
After creating an Archive Database in Exchange 2010, you find that Exchange will put new user mailboxes on this database, in order to balance mailboxes across stores. The easiest way to avoid this is to exclude the Archive Database from your mailbox provisioning.
Using Exchange 2010 Powershell, get a list of your mailbox databases by running Get-MailboxDatabase:
Once you confirm the name of your archive database, exclude it from automatic provisioning by running the following PowerShell command: Set-MailboxDatabase -Identity “Archive Database” -IsExcludedFromProvisioning $True