Basically, the Sharks entered the season with 3 legitimate NHL defenseman and a handful of bottom pairing players either looking to stick at the NHL level (Thrun, Lelhegrn, Mukha) or on their way out (Vlasic, Rutta).
The compounding issue that made this one of it not the worst D core in the league is that only Walman is a top 4 guy, Ceci and Ferraro are both legit NHL defenseman but at best you want those guys playing limited minutes and the Sharks had to give them both >20 minutes a night.
But are any of those guys playing 20 minutes a night?