According to What The Heck, Bobby?, the Astros have released nine minor league players:
Hallock, who pitched 19.1 innings for AAA Oklahoma City last season, was the closest to the majors out of any of the players released.
Walters was drafted in the 11th round of the 2011 MLB draft by the White Sox. He pitched 73.1 innings for High-A Lancaster in 2013. Walters was acquired in the 2012 Brett Myers deal.
For these nine players, their dreams of making it to the majors seems to be over. They were unconditionally released from the Astros, so other teams could theoretically pick them up, but it is unlikely.
Best of luck to these players as they move into a new phase of life.