I think everyone recognizes that the biggest problems with the OSU defense are at LB and S, so I decided to check out recruiting at those positions going back to 2008. Here are the players recruited at those positions:
2008: Sabino 5* - broken leg
2009: Bell 5* -transfer; Whiting 3* -transfer; Klein 4* - starter; Wood - no longer with team
2010: McVey 4* - medical; Durham 3* - transfer; Turner 4* - never signed; Hagan - medical
2011: Grant 5* - developing; Crowell 3* - ?; Shazier - starter; Tanner 4* - transfer; Cash 4* - transfer.
What really stands out to me is that the '09 and '10 classes, the guys who should be the upper classmen and leaders of the D, have produced one starter, Storm Klein, at LB and S, actually only one guy even in the two-deep. And there goes your personnel problem.
* edit: used Scout's data base where Pitt Brown '09, Barnett '09, and Bryant '10 are all listed as CBs