Some additional infos about the project. this but no. You definitely want to read this first. Having read this you don't want to read anything else.
New mailbox move request.
Here you can see old Legacy (from old Excange 2003) and the new, already migrated mailboxes (to a 2010 MBX server.) New mailboxes remaines green colored in this window until you don't delete manualy the succesful request, one option below.
CAS1 and CAS2 servers are in one Load Balancing Cluster. (Add it as a "feature".) Easy peasy.
Move active mailbox database you can move the db to the failover node, in this example it's called SMBX2.
A working DAG.