Washington, D.C. 20549


Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940
OMB Number: 3235-0104
Estimated average burden
hours per response: 0.5
1. Name and Address of Reporting Person*

(Last) (First) (Middle)
1001 17TH STREET, SUITE 500


(City) (State) (Zip)
2. Date of Event Requiring Statement (Month/Day/Year)
3. Issuer Name and Ticker or Trading Symbol
CoreSite Realty Corp [ COR ]
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
Director 10% Owner
X Officer (give title below) Other (specify below)
SVP, IT and Digitization
5. If Amendment, Date of Original Filed (Month/Day/Year)
6. Individual or Joint/Group Filing (Check Applicable Line)
X Form filed by One Reporting Person
Form filed by More than One Reporting Person
Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock 6,743(1)(2) D
Table II - Derivative Securities Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4) 2. Date Exercisable and Expiration Date (Month/Day/Year) 3. Title and Amount of Securities Underlying Derivative Security (Instr. 4) 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 6. Nature of Indirect Beneficial Ownership (Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Explanation of Responses:
1. Includes 4,616 shares of unvested restricted stock awards granted to the reporting person under the issuer's 2010 Equity Incentive Award Plan (the "2010 Plan"). The unvested shares vest as follows: (i) 112 shares vest on March 8, 2021, (ii) 316 shares vest in two equal annual installments beginning on March 15, 2021, (iii) 1,389 shares vest in three equal annual installments beginning on March 15, 2021, (iv) 1,212 shares vest in three equal annual installments on March 15, 2021, (v) 172 shares vest in two equal annual installments beginning on September 10, 2021, and (vi) 1,415 performance-based restricted shares ("PSAs") granted under the 2010 Plan.
2. The number of PSAs earned is based on the issuer's achievement of relative total shareholder return ("TSR") measured versus the MSCI US REIT Index over a three-year performance period ending December 31, 2023, and the number of shares earned may range from 25% to 175%. The PSAs are earned as follows: (i) 20% of the PSAs are earned upon TSR achievement in year one of the performance period, (ii) 20% of the PSAs are earned upon TSR achievement in year two of the performance period, (iii) 20% of the PSAs are earned upon TSR achievement in year three of the performance period, and (iv) 40% of the PSAs are earned upon a cumulative TSR achievement over the three-year performance period, subject to the reporting person's continued service with the issuer at the end of the three-year performance period. The PSAs are granted and issued at 175% of the target amount.
/s/ Derek S. McCandless, Attorney-in-Fact 03/10/2021
** Signature of Reporting Person Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

Know all by these presents, that the undersigned hereby constitutes and appoints
any one of Derek S. McCandless, Adam Post or Ned Prusse acting alone, as the
undersigned's true and lawful attorney-in-fact to:

(1) execute for and on behalf of the undersigned, in the undersigned's capacity
as an officer and/or director of CoreSite Realty Corporation, a Maryland
corporation (the "Company"), the Form ID and Forms 3, 4, and 5 in accordance
with Section 16(a) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act") and the rules thereunder;

(2) do and perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to complete and execute any such Form ID or Form
3, 4, or 5, complete and execute any amendment or amendments thereto, and timely
file such form with the SEC and any stock exchange or similar authority; and

(3) take any other action of any type whatsoever in connection with the
foregoing which, in the opinion of such attorney- in-fact, may be of benefit to,
in the best interest of, or legally required by, the undersigned, it being
understood that the documents executed by such attorney-in-fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form and shall
contain such terms and conditions as such attorney-in-fact may approve in such
attorney-in fact's discretion.

The undersigned hereby grants to such attorney-in-fact full power and authority
to do and perform any and every act and thing whatsoever requisite, necessary,
or proper to be done in the exercise of any of the rights and powers herein
granted, as fully to all intents and purposes as the undersigned might or could
do if personally present, with full power of substitution or revocation, hereby
ratifying and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully do or cause to be
done by virtue of this power of attorney and the rights and powers herein
granted. The undersigned acknowledges that the foregoing attorney-in-fact, in
serving in such capacity at the request of the undersigned, is not assuming, nor
is the Company assuming any of the undersigned's responsibilities to comply with
Section 16 of the Exchange Act.

This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file the Form ID or Forms 3, 4, and 5 with
respect to the undersigned's holdings of and transactions in securities issued
by the Company, unless earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be
executed as of this 26th day of February, 2021.

/s/ Aleksandra Krusko
Aleksandra Krusko