After brilliantly fulfilling his basic job description last year – see quarterback, sack quarterback – Aldon Smith will assume greater responsibility in his second NFL season.

On Wednesday, during the second day of the 49ers‘ three-day minicamp, defensive coordinator Vic Fangio ticked off Smith’s added duties as he transitions from an off-the-bench, pass-rushing specialist to a three-down outside linebacker.

Smith is expected to assume the starting role held by Parys Haralson in 2011.

He has to “master the zone coverage, where he fits in drops, picking up routes, et cetera,” Fangio said. “And also, one thing Parys was really good for us last year was playing the run. He’s got to be as good or better as Parys was, playing the run.”

Last year, Smith entered for Haralson in passing situations, lined up at defensive end, pinned his ears back and routinely caused havoc. Despite playing just 506 of 1,037 snaps (49 percent), Smith had 14 sacks, the second highest total by a rookie in NFL history.

Since Haralson excelled against the run – and Smith starred in his pass-rushing role – Fangio was asked if he has given any thought to maintaining the status quo in 2012. Fangio said Smith was simply too talented to keep him on the sideline for 50 percent of the defensive snaps.

“If it turns out that he doesn’t warrant the job with his play, then he’ll go back to that,” Fangio said. “But I think when you have a player of his ability you’ve got to do anything and everything you can to get him on the field more.”

Cox learns fast: Cornerback Perrish Cox, a free-agent signing who didn’t play last year due to legal issues (he was acquitted of sexual assault charges by a Colorado jury in March), arrived with question marks.

He’s apparently answered some of those on the field.

Fangio said he’s been impressed by Cox’s ability to learn what are, in effect, two positions. Cox has played nickel cornerback – covering the slot receiver – and played outside.

“There’s no carryover from one to the other from an assignment and technique standpoint,” Fangio said. “He’s done well learning both those positions, and we’re very happy to have him. He’s given us added depth, and he’s going to push for playing time if he continues to do the work that he’s shown so far.”

Briefly: Linebackers Patrick Willis and NaVorro Bowman again were excused from practice for personal reasons. … Tight end Delanie Walker was not at practice after suffering an undisclosed injury Tuesday. … Wide receiver Kyle Williams had the play of the day, making a lunging circus catch on a deep-in route on a throw from Alex Smith. … General manager Trent Baalke will run the Grandma’s Marathon on Saturday in Duluth, Minn. It will be his first marathon.