LTO3 is a newer format. The LTO roadmap has been pretty true to its claims, so you should get somewhere between 600-800GB per tape, depending on the data. Databases and documents will give you a better compression ration than executables and MP3 files.
Try downloading the latest driver and firware for the drives. Go to the IBM or HP website for the drivers and firmware. ADIC usually uses IBM drives. They typically only supply firmware for the robot.
Also, make sure the latest driver and firmware is applied to your initiator (SCSI or Fibre controller). If you are using a fiber controller without a fabric switch, make sure you hard code the adapter to “Arbitrated Loop”. If you are attached to a fabric switch, force the adapter to “Point – to – Point” or “Fabric”.