Can see only 4 drives out of 8 drives in the device manager

[NARAYANAMURTY RAMAYANAM]

I have a netbackup enterprise server with overland tape library which has HP LTO Gen3
Ultrium 3-SCSI.
There are total 8 drives in the library and 4 were licensed and using i got the other 4 additional licenses for the remaining drives, when i install the license key and try to use the other drives, i could not able to see them in the device manager of the Master server.
I can see only 4 drives which are active previously.
How to get other 4 drives visible in the device manager.
Every drive is FC to a switch(WWN are configured in the switch zoning).


Any help is appreciated.


Thanks
narayana