If you have an existing Fibre-Channel (FC) environment and you've recently introduced a new tape drive or library to the system you will have numerous problems with communication, backups, and restores with the tape drive. The reason for this is because zoning has not been setup on your FC Switch.
All tape devices require zoning. Without proper zoning, you will see problems of BRU Server only writing random small amounts of data to a single tape, then changing tapes. You can see BRU Server not able to change tapes at all, frequent hardware scans will be needed because the device ID in the kernel will keep changing, and the list goes on.
The reason that this doesn't work without zoning is because tape devices do not like multi-pathing. While Xsan, RAID, Xserves, and numerous other FC disk devices work fine with this, tape devices simply do not.
For assistance in zoning, you'll need to contact your FC switch manufacturer for the setup required by that make and model of FC switch.