Catalyzes the production and accumulation of glycerol during hyperosmotic stress conditions. Glycerol acts as a osmoregulator that prevents loss of water and turgor of the cells. NAD(+) + sn-glycerol 3-phosphate = dihydroxyacetone phosphate + H(+) + NADH By osmotic stress and by methylglyoxal in a HOG pathway-dependent manner. Present with 807 molecules/cell in log phase SD medium. Belongs to the NAD-dependent glycerol-3-phosphate dehydrogenase family. Was originally thought to be GUT2, the FAD-dependent glycerol-3-phosphate dehydrogenase.