EXHIBIT 2

JOINT FILING AGREEMENT

The undersigned hereby agree to the joint filing of the Amendment No. 1 to Schedule 13D to which this Agreement is attached.

Dated:  February 8, 2011

DISCOVERY GROUP I, LLC

By Michael R. Murphy*                                                           

      Michael R. Murphy

      Managing Member

Daniel J. Donoghue*                                                                 

Daniel J. Donoghue

Michael R. Murphy*                                                                  

Michael R. Murphy

*By: /s/ Mark Buckley                                                              

         Mark Buckley

         Attorney-in-Fact for Daniel J. Donoghue

         Attorney-in-Fact for Michael R. Murphy