Here is a 27 point mesh I generated using Professor David Lewis' "PLOP" program.  This one is for a 10" mirror with a 1.3" Secondary mirror, a 54" focal length, and a thickness of 2 inches.
The supporting points can be seen in the mesh.  You can see these points more clearly by merely placing your mouse pointer over this link Put your mouse over this link to see how varius triangles are used to position the supports.
Touching this link will leave you looking at the colour map of the mirror's surface deformations when used with this support structure. Each colour represents a different wavefront error. The Red zones are areas of extremely poor wavefront error.  The Blue areas coincide with the location of the supports.
Every second time you place your mouse over this link you toggle the image between a 9 point cell's triangular supports and a colour map of how the above mirror deforms using 9 points instead of 27 points.