I would suggest following. Attach LTO3 library to the server while still having CDL+LTO1 combination. Stage all data that you need from LTO1 to LTO3 tapes including data on CDL only (otherwise you will probably loose it during CDL reconfiguration). Once you migrated data to LTO3, you can remove LTO1 from backend and place LTO3 and then reconfigure CDL. Of course, it would be a bit tricky what to do if you need to do a restore from migrated data (as "new" CDL library would not be aware of that and physical library would be on the backend) but I guess you could always have one drive presented somehow to server as standalone. Or you simply go for option to keep data until it is not expired (this really depends on policy you use). Of course, tapes you used for migration would need to be put away from CDL until they are ready to be used again.