Complex sentence: The mid- 2010 Server model was initially the only Mac Mini to entirely remove the optical drive, replacing it with a second hard drive in its place, however from the mid- 2011 models onwards, all models of Mac Mini had the optical drive removed.
Split into simpler sentences: The mid- 2010 Server model was initially the only Mac Mini to entirely remove the optical drive, replacing it with a second hard drive in its place. However, from the mid- 2011 models onwards, all models of Mac Mini had the optical drive removed.