OST media server config question ..

Yes the OST Opt-Dup reduces workload on the NetBackup Media servers.  However, you need to let Media Servers from one site to be able to "see" both OST appliance so the SLP job can be established.

Here are the Opt-Dup requirements from NetBackup Shared Storage Guide:

• The vendor must expose the off-host data movement capability in their plug-in.
• Both the source and the destination disk pools must be the same OpenStorage vendor type.
• One or more NetBackup media servers must connect to the source appliance and the destination appliance.

Once the communication of both ends are established, the SLP data replications are done by the OST appliances.

I usually add all the OST appliances/storage_servers' credentials to the Prod site Media Servers so they can "see" both OST appliances, while the DR site Media Servers only have the DR site OST appliance's credentials, since the replication traffic is one way from Prod site to DR site.

Another thing you need to be aware - to avoid the primary backups (not the backup duplication/replication) across WAN to the remote site OST appliance, I selected "Only use the following media servers" in the OpenStorage STU and unselected the remote site media servers.