The rear discs will be unvented, the fronts vented hence much thicker. I do not have the data abouyt minimum brake disc thickness for a CRV, but as a general guide have a look see and feel of the wear ...
Disc brakes work using a simple system: brake pads contained within the caliper (the clamp-like object around the brake rotor, or disc) apply pressure to the rotor and slow the car when you press the ...