Clio 200 rear disc has a lip

My clio 200 has done 17k miles now and my drivers side rear disc has a lip on it, it's about halfway down the face of the disc, I know I need new pads in the next few thousand miles but what will be the cause of this ? Discs won't be worn out after 17k miles ?
 
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there might be a piece of the pad surface missing and hence why the lip has appeared on the disc face - the disc will wear to the pad surface
 
Ok cheers, will this be fine if I put new pads on ?

it will just mean the disc with the lip will make the pad wear odd until its worn down but it may suffer with unusal wear... until a new disc is fitted - best investigate why it has gone like that BEFORE fitting new
 
it may also cause vibration on the pad so may squeal like mad under braking, aka like a bus.