Providing more details will probably result in faster better replies instead of my reply like this one asking for more details.
Hardware used? Can you access these tape drives manually? Any particular logs that might tell you what's happening with more details? Are you sure nothing is accessing the drives when you try to use them within Legato? Are the drives even working or configured? Have these ever worked in Legato or any other software/hardware setup? Is this a new install of Legato? Anything else you can think of, shoe size, current breath smell and so on is helpful at all times instead of the very vague question you've asked without such details..
