You're absolutely right, it's LTO, not DLT and they are all the same. And I agree about the capacity, having thought about it now, in which case it's doing exactly what it should be. I will have a proper read up on it so that I know exactly what the state of play is. We can't practically go above three tapes per set, so if they are approaching capacity, I'll have to archive some of the data on the RAID. Anyway, it looks like it probably was just an error on the third tape, and it is an isolated incident. I guess I'll find out in four weeks time! If it does go wrong again, I'll replace the tapes. Thank you so much for your help.