When I'm applying a brake there is coming strange sound from left front wheel. My guess was that it's coming from brakes, so I disassemble the wheel. Below is a picture of breaking pads and rotor from this wheel. There is strange texture on rotors.
I would like to ask if It's necessary to change both, pads and rotors, or can I change just pads, based on picture. In simple words, is rotor still usable?