Configuring Optimised Duplication within the same NetBackup domain

Hello

I'm trying to configure optimised replication between a master server (that also acts as a media server) and another media server. These are the only two NetBackup servers within the domain. Both have MSDPs and the media server has a tape library attached. I want the backups that are occuring on the master server's MSDP to be duplicated to the media server where it can then be written to tape.

The problem I'm having is around setting up the 'common' media server as I don't really understand what I need to do to create this. Currently the two MSDPs are independent  - by which I mean that only the 'owning' media server has access to it. This was configured this way when the Storage Servers were first created. So now I think I need to reconfigure this so that the media server (with the attached tape library) can 'pull' the data from the Master\Media server's MSDP pool to it's own MSDP. How do I set the credentials to do this? If I look at the properties of the storage server I can see both servers in the list but with only one checkbox selected. However, if I select both check boxes and apply that I then don't see the option for the server in the Storage Unit - and it's here that I think I need to create the 'common' media server.

many thanks