It may come as some surprise to you, or it may not, that Jeff Luhnow is the 2nd longest-tenured GM in Astros history. Here are the tenures of Astros GMs:
Gerry Hunsicker: November 1995-November 2004 (9 seasons)
Spec Richardson: 1967-1975 (almost 9 seasons)
Jeff Luhnow: December 2011-present (currently 8 seasons)
Tal Smith: 1975-1980, 2007 (6 seasons)
Al Rosen: 1980-1985: (5 seasons)
Paul Richards: 1962-1965 (3 seasons)
Tim Purpura: 2004-2007 (3 seasons)
Dick Wagner: 1985-1987 (2 seasons)
Let's take a look at the trades Luhnow has made, evaluating them based on the fWAR he traded away, and the fWAR he received.