Double side vs single side faces rendering costs

Hi, i was trying to understand if using double sided shader is much expensive of single side shader.

I was thinking about a sphere, you want to let the user see the texture when is inside and outside its volume,

  1. Is the geometry duplicated and flipped automatically to have the normals facing the other side (this is the less performant and probably less thinkable implementation for sure)
  2. Or the shader/api/graphic card simply ignore the direction of the normals vector to check face visibility?
  3. Any other tetchnique?

I didn’t find ay informations about its implementation at lower levels.