Pay attention to which side of the OSB you want exposed...smooth or traction side. Traction side can be a PIA when trying to slide heavy boxes into place, or removing from storage.
I have a shelving unit 24" deep by 8' wide covered with 1/2" OSB in my garage. There is a lot of crapola on these shelves with zero deflection. Back wall is 1x4, front and side framing is 2x4 with drywall screws. The 8' unit only has end framing and is attached at the center post, and I have zero sag with the 1/2" OSB shelving that is held down with 1-1/4" drywall screws. OSB is pretty darn tough, and screwing it in place every 12" or so will keep it flat and add to the rigidity of the shelf unit.