ssh/telnet into the switch and run:  sh zoneset active vsan   | grep   | wc -l
Hello,  Our backup admin asked me how to tell if the what hosts are zoned to the tape library in fabric manager. I tried to do a search within the grey box, but it did not return anything. Short of counting each zone we think has it attached, I did not see a way to report this info.  Thanks in advance,  Happy admin! 
how to tell how many hosts are zoned to a tape drive in fabric manager