Backup exec creates a "backup set" for each device selected to be backed up. For example, if you are backing up the c and d drives for 2 servers (server1 and server2), the backup will create 4 backup sets.
server1 c drive = backup set 1
server1 d drive = backup set 2
server2 c drive = backup set 3
server2 d drive = backup set 4
If you run the same backup of the above onto the same tape (appending to the tape) the backup sets will increment each time. Eg
server1 c drive = backup set 5
server1 d drive = backup set 6
etc
You have the "max number of backup sets per backup to disk file" set to 100, once it reaches this limit it will create a new backup to disk file (bkf file). You can change this setting from the range of 1 to 8192.
As for the "storage media #2", this is telling you that the backup is writing to the second backup to disk file for the media family.