Ah, ha! Now, from your question to the OP, I think I understand what he was asking.
You don't mean "lines" do you(?) ... you mean rings. Lines are straight dude, rings are circular. I think what you are asking about is why you are getting rings of unburned areas on your backup media. Right.
I'm sure my answer is what sonoluca is prepared to answer when you get back to responding to this thread you started ... I guess you went walkabout for 20 hours
Those rings are caused by the buffer in your drive going empty resulting in the sorry condition that your burner has no data to burn for a second or a fraction of a second. This is most often caused by too high a burn speed for the data transfer from your backup software to the burner. It can become an especially apparent problem when using an externally connected burner like you have ... due to data transfer delays along the motherboard's channels to and from the processor and out the output channels and cables to your external burner. Internal burners are better for making problem free backups ... but there is a solution.
Slow down your burn speed so your burner is not trying to burn at a speed faster than it's buffer can suck the data in from your computer's bus transfer rate. In other words, your burner's buffer should never go empty or have wild fluctuations in the amount of data being held, "ready to burn", in the buffer. Under those undesirable conditions, you will get "unburned" rings on your backup media and the media will be unplayable. I.E, your burner needs a nice, static "puddle" of data to draw upon while burning at a specified speed. This "puddle" is what a buffer provides. And it must always be full and never go "dry".
Slow down your burn speed or mount your burner on an internal IDE channel which handles fast data transfers better.
BTW another reason for buffer under-runs is that the user is doing other tasks on the computer while the burn is going on. Don't surf the web or be doing other multi-tasking chores during a burn! :disagree: Just walk away from your computer until your backup is complete. If you are the kind of person who can't do this, consider building another box just for making backups so you can do your other work on your main computer.