FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * Carlyle Realty III, GP, L.L.C.   2. Issuer Name and Ticker or Trading Symbol CoreSite Realty Corp [COR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O THE CARLYLE GROUP, 1001 PENNSYLVANIA AVE. NW, SUITE 220S 3. Date of Earliest Transaction (Month/Day/Year) 05/01/2015 (Street) WASHINGTON, DC 20004 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/01/2015   M   4,500,000 A (1) 4,500,000 I See footnotes (2) (3) (4) Common Stock 05/01/2015   S   4,500,000 D $ 48.67 0 I See footnotes (2) (3) (4)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Operating Partnership Units

(1)

05/01/2015

M

4,500,000

(1)

(1)

Common Stock

4,500,000

(1)

20,775,390

I

See footnotes (2) (3) (4)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Carlyle Realty III, GP, L.L.C. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
Carlyle Realty III, L.P. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CoreSite CRP III Holdings, LLC C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CRP III AIV GP, L.L.C. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CRP III AIV GP, L.P. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CRQP III AIV, L.P. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CoreSite CRP III Holdings (VCOC), LLC C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
Carlyle Realty IV GP, L.L.C. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
Carlyle Realty IV, L.P. C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X
CoreSite CRP IV Holdings, LLC C/O THE CARLYLE GROUP 1001 PENNSYLVANIA AVE. NW, SUITE 220S WASHINGTON, DC 20004		X

Signatures

/s/ R. Rainey Hoffman, attorney-in-fact for Daniel A. D'Aniello, Chairman		05/05/2015
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The operating partnership units are redeemable at any time for cash or, at the election of the Issuer, exchangeable for shares of common stock on a one-for-one basis, and have no expiration date.
(2)	Following the transactions reported herein, consists of (i) 5,114,769 common units held by CoreSite CRP III Holdings, LLC; (ii) 1,036,123 common units held by CoreSite CRP III Holdings (VCOC), LLC; (iii) 3,584,431 common units held by CoreSite CRP IV Holdings, LLC; (iv) 610,419 common units held by CoreSite CRP IV Holdings (VCOC I), LLC; (v) 1,568,923 common units held by CoreSite CRP IV Holdings (VCOC II), LLC; and (vi) 8,860,725 common units held by CoreSite CRP V Holdings, LLC.
(3)	Carlyle Group Management L.L.C. is the general partner of The Carlyle Group L.P., which is a publicly traded entity listed on NASDAQ. The Carlyle Group L.P. is the sole shareholder of Carlyle Holdings I GP Inc., which is the managing member of Carlyle Holdings I GP Sub L.L.C., which is the general partner of Carlyle Holdings I L.P., which is the managing member of TC Group, L.L.C., which is the general partner of TC Group Sub L.P., which is the managing member of each of Carlyle Realty III GP, L.L.C., CRP III AIV GP, L.L.C., Carlyle Realty IV GP, L.L.C., CRP IV AIV GP, L.L.C. and Carlyle Realty V GP, L.L.C.
(4)	Carlyle Realty III GP, L.L.C. is the general partner of Carlyle Realty III, L.P. which is the manager of CoreSite CRP III Holdings, LLC. CRP III AIV GP, L.L.C. is the general partner of CRP III AIV GP, L.P., which is the general partner of CRQP III AIV, L.P., which is the managing member of CoreSite CRP III Holdings (VCOC), LLC. Carlyle Realty IV GP, L.L.C. is the general partner of Carlyle Realty IV, L.P., which is the manager of CoreSite CRP IV Holdings, LLC. CRP IV AIV GP, L.L.C. is the general partner of CRP IV AIV GP, L.P., which is the general partner of each of CRP IV-A AIV, L.P. and CRQP IV AIV, L.P., which are the managing members of CoreSite CRP IV Holdings (VCOC I), LLC and CoreSite CRP IV Holdings (VCOC II), LLC, respectively. Carlyle Realty V GP, L.L.C. is the general partner of Carlyle Realty V, L.P., which is the manager of CoreSite CRP V Holdings, LLC.
Remarks: Due to the limitations of the electronic filing system Carlyle Group Management L.L.C., The Carlyle Group L.P., Carlyle Holdings I GP Inc., Carlyle Holdings I GP Sub L.L.C., Carlyle Holdings I L.P., TC Group, L.L.C., TC Group Sub L.P., CRP IV AIV GP, L.L.C., CRP IV AIV GP, L.P., CRP IV-A AIV, L.P., CRQP IV AIV, L.P., CoreSite CRP IV Holdings (VCOC I), LLC, CoreSite CRP IV Holdings (VCOC II), LLC, Carlyle Realty V GP, L.L.C., Carlyle Realty V, L.P. and CoreSite CRP V Holdings, LLC. are filing a separate Form 4.

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