VNET [21Vianet] SC 13G: JOINT FILING AGREEMENT Dated: February 2, 2012 Matrix
[JOINT FILING AGREEMENT Dated: February 2, 2012 Matrix Partners China I, L.P. David Su Director Matrix Partners China I-A, L.P. David Su Director Matrix China Management I, L.P. David Su Director Matrix China I GP GP, Ltd. David Su] [SCHEDULE 13G (Rule 13d–102) (Amendment No. _________) * 21Vianet Group, Inc. (Name of Issuer) Class A Ordinary Shares, par value US$0.00001 per share (Title of Class of Securities) 90138A 10 3 (CUSIP Number) December 31, 2011 (Date of Event Which Requires Filing of this Statement) o Rule 13d-1(b) o Rule 13d-1(c) x Rule 13d-1(d) *The remainder of this cover page]