Consider the block matrix $M = \begin{pmatrix} A & B \\ C & D \end{pmatrix}$ with $A = 2I_2$, $B = I_2$, $C = I_2$, $D = 3I_2$ where $I_2$ is the $2 \times 2$ identity. The Schur complement is $S = D - CA^{-1}B$. Which statements are correct?