Exhibit 99

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) promulgated under the Securities and Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing with each other on behalf of each of them of such a statement on Schedule 13G with respect to the Common Stock beneficially owned by each of them of CoreSite Realty Corporation. This Joint Filing Agreement shall be included as an Exhibit to such Schedule 13G.

IN WITNESS WHEREOF, the undersigned hereby execute this Joint Filing Agreement as of the 14^th day of February, 2013.

CARLYLE GROUP MANAGEMENT L.L.C.
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
THE CARLYLE GROUP L.P.
By: Carlyle Group Management L.L.C., its general partner
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE HOLDINGS I GP INC.
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE HOLDINGS I GP SUB L.L.C.
By: Carlyle Holdings I GP Inc., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE HOLDINGS I L.P.
By: Carlyle Holdings I GP Sub L.L.C., its general partner
By: Carlyle Holdings I GP Inc., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

TC GROUP, L.L.C.
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
TC GROUP SUB L.P.
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE REALTY V GP, L.L.C.
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE REALTY V, L.P.
By Carlyle Realty V GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CORESITE CRP V HOLDINGS, LLC
By: Carlyle Realty V, L.P., its managing member
By Carlyle Realty V GP, L.L.C., its General Partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

CARLYLE REALTY III, GP, L.L.C.
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE REALTY III, L.P.
By: Carlyle Realty III, GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CORESITE CRP III HOLDINGS, LLC
By: Carlyle Realty III, L.P., its managing member
By: Carlyle Realty III, GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CRP III AIV GP, L.L.C.
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

CRP III AIV GP, L.P.
By: CRP III AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CRQP III AIV, L.P.
By: CRP III AIV GP, L.P., its general partner
By: CRP III AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CORESITE CRP III HOLDINGS (VCOC), LLC
By: CRQP III AIV, L.P., its managing member
By: CRP III AIV GP, L.P., its general partner
By: CRP III AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CARLYLE REALTY IV GP, L.L.C.
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

CARLYLE REALTY IV, L.P.
By: Carlyle Realty IV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CORESITE CRP IV HOLDINGS, LLC
By: Carlyle Realty IV, L.P., its managing member
By: Carlyle Realty IV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CRP IV AIV GP, L.L.C.
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CRP IV AIV GP, L.P.
By: CRP IV AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

CRP IV-A AIV, L.P.
By: CRP IV AIV GP, L.P. , its general partner
By: CRP IV AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CoreSite CRP IV Holdings (VCOC I), LLC
By: CRQP IV AIV, L.P., its managing member
By: CRP IV AIV GP, L.P., its general partner
By: CRP IV AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CRQP IV AIV, L.P.
By: CRP IV AIV GP, L.P., its general partner
By: CRP IV AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman
CORESITE CRP IV HOLDINGS (VCOC II), LLC
By: CRQP IV AIV, L.P. , its managing member
By: CRP IV AIV GP, L.P., its general partner
By: CRP IV AIV GP, L.L.C., its general partner
By: TC Group Sub, L.P., its managing member
By: TC Group, L.L.C., its general partner
By: Carlyle Holdings I L.P., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Chairman

DBD INVESTORS V HOLDINGS, L.L.C.
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Managing Director
DBD INVESTORS V, L.L.C.
by: DBD Investors V Holdings, L.L.C., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Managing Director
TCG HOLDINGS II, L.P.
by: DBD Investors V, L.L.C., its general partner
by: DBD Investors V Holdings, L.L.C., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Managing Director
TC GROUP INVESTMENT HOLDINGS, L.P.
by: TCG Holdings II, L.P., its general partner
by: DBD Investors V, L.L.C., its general partner
by: DBD Investors V Holdings, L.L.C., its managing member
By:	/s/ R. Rainey Hoffman, attorney-in-fact
Name:	Daniel D’Aniello
Title:	Managing Director