A related discussion:
https://www-secure.symantec.com/connect/forums/multipathing-fiber-switches-netbackup
A 2-port FC HBA is still a single point of failure, best to have two separate FC HBAs on the media server connecting to the tape library.
Zone half the tape drives to each HBA. E.g., if you have say 8 tape drives, zone 4 to HBA1, and the remaining 4 to HBA2.
This way, if one of the HBA fails, it wouldn't bring all 8 drives down with it. You'd still have access to the remaining 4 drives through the remaining HBA. This also forces the media server to load balance between the two HBAs, somewhat.
Although Nbu supports multi-path to the same tape drive, it is generally not a good idea to zone each HBA to all 8 drives. Since multipath path selection is not dynamic, Nbu will select the first available path it finds and sticks to it. This means that if you zone each HBA to all 8 drives, then there is a chance that all or most load would only go through one HBA if Nbu happens to select the paths to the drives through that HBA.
But then of course, in this case, if one of your HBA dies, then the remaining HBA would still have access to all 8 drives. (I think a single HBA would have a hard time feeding 8 tape drives all at once...)
If you have the SSO feature covered in your license, then you can zone the drives to other media servers too; if you have other media servers. (SSO is licensed per drive)
Some tape drives have two FC ports for failover. They are usually for going through separate FC switches. Apparently some are not active active, and therefore would be of little use to Nbu.
As for the robot (robot control path), unlike tape drives, you cannot zone it to multiple media servers.
However, you can zone it to more than one HBA on the same media server.
People usually let the master server control the robot because, in practice, your master server should be the most resilient server compared to other media servers. (If your environment only has one master server that is also running as a media server, then just zone the robot to it)
The steps to zone the robot control path to multiple HBAs on the same media server:
http://www.symantec.com/business/support/index?page=content&id=TECH60395
