Couple things you need to understand.
1st, the OS (where NBU Media server is on) needs to be able to see the drives before your NBU media server can see them.
- so, run hardware scan (Windows Device Manager -> scan for hardware change), or sgscan (Solaris), or ioscan (HP-UX), etc. to see if the OS can see the drives.
- if the OS saw drives are missing, you need to troubleshoot that part first. Reset your HBA port links if the tape drives are on SAN. IF that doesn't solve the problem, reset the FC
ports on the tape library (they usually have I/O blade cards for FC connection).
- after the FC links have been reset, try the sgscan/ioscan/etc. again and see if the OS can see the drives now.
- also check your HBA"s persistent binding configuration - it is important to understand that FC SAN is changed frequently (which is not a problem for SAN disk, but a problem for SAN tape), so persistent binding of your HBA port to the tape library's I/O port will help you A LOT!!
If the OS can see the drives fine, then you should be able to bring up the drives if the devices were configured correctly in NBU. Make sure you followed the NBU Device Configuration Guide to configure them. (http://seer.entsupport.symantec.com/docs/290200.htm)