GUARANTY

Exhibit 10.2

GUARANTY

Project Commonly Known as

“Data Center Facility, CH1, Elk Grove Village, Illinois”

THIS GUARANTY (“ Guaranty ”) made as of December 20, 2007, by DUPONT FABROS TECHNOLOGY, L.P., a Maryland limited partnership (“ Guarantor ”), to and for the benefit of KEYBANK NATIONAL ASSOCIATION (“ KeyBank ”), a national banking association, as Agent (“ Agent ”), and KeyBank and the other lenders now or hereafter a party to the Loan Agreement (as hereinafter defined) (the “ Lenders ”) (Agent and the Lenders, and their successors and assigns, are hereinafter referred to collectively as the “ Credit Parties ”).

R E C I T A L S

A. On or about the date hereof, Tarantula Ventures LLC, a Delaware limited liability company (“ Borrower ”), Agent and the Lenders entered into that certain Construction Loan Agreement (the “ Loan Agreement ”) whereby the Lenders agreed to make a secured construction loan (the “ Loan ”) available to Borrower in the maximum aggregate amount at any time outstanding not to exceed the sum of One Hundred Forty-Eight Million Eight Hundred Sixty-Four Thousand Three Hundred Thirty-Five and no/100 Dollars ($148,864,335.00), to finance the development and construction of a data center facility to consist when fully completed of approximately 485,000 gross square feet, and 211,140 raised square feet with a critical load of 36.4 megawatts (the first phase will consist of approximately 121,223 raised square feet with a critical load of 18.2 megawatts) (the “ Project ”). Capitalized terms used and not otherwise defined herein shall have the meanings given to them in the Loan Agreement.

B. In connection with the Loan, Borrower has executed and delivered the Notes in favor of Lenders, payment of which is secured by (i) the Mortgage, and (ii) the other Loan Documents.

C. Guarantor will derive material financial benefit from the Loan evidenced and secured by the Notes, the Mortgage and the other Loan Documents.

D. The Credit Parties have relied on the statements and agreements contained herein in agreeing to make the Loan. The execution and delivery of this Guaranty by Guarantor is a condition precedent to the making of the Loan by Lenders.

AGREEMENTS

NOW, THEREFORE, intending to be legally bound, Guarantor, in consideration of the matters described in the foregoing Recitals, which Recitals are incorporated herein and made a part hereof, and for other good and valuable consideration the receipt and sufficiency of which are acknowledged, hereby covenants and agrees for the benefit of the Credit Parties and their respective successors, indorsees, transferees, participants and assigns as follows:

1. Guarantor, absolutely, unconditionally, and irrevocably guarantees:

(a) subject to the terms of Section 22 below, (a) the full and prompt payment of the principal of and interest on the Notes when due, whether at stated maturity, upon

acceleration or otherwise, and at all times thereafter, and the full and prompt payment of all sums which may now be or may hereafter become due and owing under the Notes, the Loan Agreement and the other Loan Documents;

(b) the full, complete and punctual observance, performance and satisfaction of all of the obligations, duties, covenants and agreements of Borrower under the Loan Agreement and the other Loan Documents with respect to the Construction and completion of the Project free of any claim for mechanics’, materialmen’s or any other liens, and in accordance with (i) all Laws, (ii) the Plans and Specifications and (iii) the time periods and other requirements set forth in the Loan Documents, including, without limitation, the following:

(A) To perform, complete and pay for (or cause to be performed, completed and paid for) the Construction and to pay all costs of said Construction (including any and all cost overruns) and all other costs associated with the Project (including, without limitation, the costs of any architects’ and engineers’ fees), if Borrower shall fail to perform, complete or pay for such work, including any sums expended in excess of the amount of indebtedness incurred by Borrower under the Loan Agreement or with respect to the Loan, whether or not the Construction is actually completed;

(B) If the Credit Parties exercise their right under Section 20.1(a) of the Loan Agreement to take possession of the Project and complete the Construction, to reimburse the Credit Parties for all costs and expenses incurred by the Credit Parties in excess of the applicable Budget Line Items therefor (if any) in so taking possession of the Project and completing the Construction pursuant to the Plans and Specifications;

(C) If any mechanics’ or materialmen’s liens should be filed, or should attach, with respect to the Project by reason of the Construction, to promptly cause the removal of such liens, or post security against the consequences of their possible foreclosure and procure an endorsement(s) to the title policy insuring the Credit Parties against the consequences of the foreclosure or enforcement of such lien(s);

(D) If any chattel mortgages, conditional vendor’s liens or any liens, encumbrances or security interests whatsoever should be filed, or should attach, with respect to the personal property, fixtures, attachments and equipment delivered upon the Project and owned by Borrower, attached to the Project or used in connection with the construction of the Improvements, to promptly cause the removal of such lien(s) or post security against the consequences of their possible foreclosure and procure an endorsement(s) to the title policy insuring the Credit Parties against the consequences of the foreclosure or enforcement of such lien(s); and

(E) To pay the premiums for all policies of insurance required to be furnished by Borrower pursuant to the Loan Agreement during the Construction if such premiums are not paid by Borrower;

(c) Borrower’s obligation to keep the Loan In Balance (as more particularly defined and described in Article 11 of the Loan Agreement) and the full and prompt payment of all Deficiency Deposits;

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(d) the full, complete and punctual observance, performance and satisfaction of all of the other obligations, duties, covenants and agreements of Borrower under the Loan Agreement and the Loan Documents; and

(e) the full and prompt payment of any Enforcement Costs (as hereinafter defined in Section 7 hereof).

All amounts due, debts, liabilities, payment obligations and other obligations described in subsections (a) through (d) of this Section 1 are referred to herein as the “Obligations.”

2. In the event of any default by Borrower in the payment or performance of the Obligations and the expiration of any applicable cure or grace period, Guarantor agrees, on demand by Agent or the Credit Parties (which demand may be made concurrently with notice to Borrower that Borrower is in default of its obligations), to pay and perform all the Obligations regardless of any defense, right of setoff or claims which Borrower or Guarantor may have against any of the Credit Parties. The Credit Parties shall have the right, at their option, either before, during or after commencing foreclosure or sale proceedings, as the case may be, and before, during or after pursuing any other right or remedy against Borrower or Guarantor, to perform any and all of the Obligations by or through any agent, contractor or subcontractor of its selection, all as the Credit Parties in their sole discretion deem proper, and Guarantor shall indemnify and hold the Credit Parties free and harmless of, and against any and all loss, damage, cost, expense, injury, or liability the Credit Parties may suffer or incur in connection with the exercise of their rights under this Guaranty or the performance of the Obligations. Furthermore, the Credit Parties shall not have any obligation to protect or insure any collateral for the Loan, nor shall the Credit Parties have any obligation to perfect their security interest in any collateral for the Loan.

During the course of any construction undertaken by the Credit Parties or any other party on behalf of the Credit Parties in accordance with the terms of this Guaranty, Guarantor shall pay on demand any amounts due to contractors, Subcontractors, and material suppliers and for permits and licenses necessary or desirable in connection therewith. Guarantor’s obligations in connection with such work shall not be affected by any errors or omissions of the General Contractor, Architect, Engineer, Lender’s Consultant or any Subcontractor or agent or employee of any of the foregoing in the design, supervision, and performance of the work; it being understood that such risk is assumed by Guarantor. Neither the completion of the Construction nor failure of said party to complete the Construction shall relieve Guarantor of any liabilities hereunder; rather, such liability shall be continuing and may be enforced by the Credit Parties to the end that the Construction shall be timely completed, lien-free, without loss, cost, expense, injury or liability of any kind to the Credit Parties.

All of the remedies set forth herein and/or provided for in any of the Loan Documents or at law or equity shall be available to the Credit Parties, and the choice by the Credit Parties of one such alternative over another shall not be subject to question or challenge by Guarantor or any other Person, nor shall any such choice be asserted as a defense, setoff, or failure to mitigate damages in any action, proceeding, or counteraction by the Credit Parties to recover or seeking any other remedy under this Guaranty, nor shall such choice preclude the Credit Parties from subsequently electing to exercise a different remedy. The parties have agreed to the alternative remedies hereinabove specified in part because they recognize that the choice of remedies in the

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event of a failure hereunder will necessarily be and should properly be a matter of good faith business judgment, which the passage of time and events may or may not prove to have been the best choice to maximize recovery by the Credit Parties at the lowest cost to Borrower and/or Guarantor. It is the intention of the parties that such good faith choice by the Credit Parties be given conclusive effect regardless of such subsequent developments.

3. Guarantor hereby agrees that its obligations hereunder shall not be affected or impaired by, and hereby waives and agrees not to assert or take advantage of any defense based on:

(a) (i) any change in the amount, interest rate or due date or other term of any of the obligations hereby guaranteed, (ii) any change in the time, place or manner of payment of all or any portion of the obligations hereby guaranteed, (iii) any amendment or waiver of, or consent to the departure from or other indulgence with respect to, the Loan Agreement, any other Loan Document, or any other document or instrument evidencing or relating to any obligations hereby guaranteed, or (iv) any waiver, renewal, extension, addition, or supplement to, or deletion from, or any other action or inaction under or in respect of, the Loan Agreement, any of the other Loan Documents, or any other documents, instruments or agreements relating to the obligations hereby guaranteed or any other instrument or agreement referred to therein or evidencing any obligations hereby guaranteed or any assignment or transfer of any of the foregoing;

(b) any subordination of the payment of the obligations hereby guaranteed to the payment of any other liability of Borrower or any other person;

(c) any act or failure to act by Borrower or any other Person which may adversely affect Guarantor’s subrogation rights, if any, against Borrower or any other Person to recover payments made under this Guaranty;

(d) any nonperfection or impairment of any security interest or other lien on any collateral, if any, securing in any way any of the obligations hereby guaranteed or any failure on the part of the Credit Parties to ascertain the extent or nature of any collateral or any insurance or other rights with respect thereto, or the liability of any party liable under the Loan Documents or the obligations evidenced or secured thereby;

(e) any application of sums paid by Borrower or any other Person with respect to the Obligations, regardless of what liabilities of Borrower remain unpaid;

(f) any defense of Borrower, including without limitation, the invalidity, illegality or unenforceability of any of the Obligations;

(g) either with or without notice to Guarantor, any renewal, extension, modification, amendment or another changes in the Obligations, including but not limited to any material alteration of the terms of payment or performance of the Obligations;

(h) any statute of limitations in any action hereunder or for the collection of the Notes or for the payment or performance of any obligation hereby guaranteed;

(i) the incapacity, lack of authority, death or disability of Borrower or any other Person or entity, or the failure of the Credit Parties to file or enforce a claim against the estate (either in administration, bankruptcy or in any other proceeding) of Borrower or Guarantor or any other Person;

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(j) the dissolution or termination of existence of Borrower, Guarantor or any other Person;

(k) the voluntary or involuntary liquidation, sale or other disposition of all or substantially all of the assets of Borrower or Guarantor or any other Person;

(l) the voluntary or involuntary receivership, insolvency, bankruptcy, assignment for the benefit of creditors, reorganization, assignment, composition, or readjustment of, or any similar proceeding affecting, Borrower or Guarantor or any other Person, or any of Borrower’s or Guarantor’s or any other Person’s properties or assets;

(m) an assertion or claim that the automatic stay provided by 11 U.S.C. §362 (arising upon the voluntary or involuntary bankruptcy proceeding of Borrower) or any other stay provided under any other debtor relief law (whether statutory, common law, case law or otherwise) of any jurisdiction whatsoever, now or hereafter in effect, which may be or become applicable, shall operate or be interpreted to stay, interdict, condition, reduce or inhibit the ability of the Credit Parties to enforce any of their rights, whether now or hereafter required, which the Credit Parties may have against Guarantor or any collateral for the Loan;

(n) any right or claim of right to cause a marshaling of the assets of Borrower or Guarantor;

(o) the damage, destruction, condemnation, foreclosure or surrender of all or any part of any collateral or the Project or any of the improvements located thereon;

(p) the failure of the Credit Parties to give notice of the existence, creation or incurring of any new or additional indebtedness or obligation of Borrower or of any action or nonaction on the part of any other person whomsoever in connection with any obligation hereby guaranteed;

(q) any failure or delay of the Credit Parties to commence an action against Borrower or any other Person, to assert or enforce any remedies against Borrower under the Notes or the other Loan Documents, or to realize upon any security;

(r) any failure of any duty on the part of the Credit Parties to disclose to Guarantor any facts they may now or hereafter know regarding Borrower (including, without limitation Borrower’s financial condition), any other person or entity, any collateral, or any other assets or liabilities of such person or entity, whether such facts materially increase the risk to Guarantor or not (it being agreed that Guarantor assume responsibility for being informed with respect to such information);

(s) failure to accept or give notice of acceptance of this Guaranty by the Credit Parties;

(t) failure to make or give notice of presentment and demand for payment of any of the indebtedness or performance of any of the obligations hereby guaranteed;

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(u) failure to make or give protest and notice of dishonor or of default to Guarantor or to any other party with respect to the indebtedness or performance of obligations hereby guaranteed;

(v) any and all other notices whatsoever to which Guarantor might otherwise be entitled;

(w) any lack of diligence by the Credit Parties in collection, protection or realization upon any collateral securing the payment of the indebtedness or performance of obligations hereby guaranteed;

(x) the invalidity or unenforceability of the Notes, or any of the other Loan Documents, or any assignment or transfer of the foregoing;

(y) the compromise, settlement, release or termination of any or all of the obligations of Borrower under the Notes or the other Loan Documents;

(z) any transfer by Borrower or any other Person of all or any part of the security encumbered by the Loan Documents;

(aa) any right to require the Credit Parties to proceed against Borrower or any other Person or to proceed against or exhaust any security held by the Credit Parties at any time or to pursue any other remedy in the Credit Parties’ power or under any other agreement before proceeding against Guarantor hereunder or under any other Loan Document;

(bb) the failure of the Credit Parties to perfect any security or to extend or renew the perfection of any security;

(cc) any principle or provision of law, statutory or otherwise, which is or might be in conflict with the terms and provisions of this Guaranty;

(dd) any inaccuracy of any representation or other provision contained in any Loan Document;

(ee) any sale or assignment of the Loan Documents, or any interest therein;

(ff) any and all rights, benefits and defenses which might otherwise be available under the provisions of any other applicable statues, rules or common law principals or provisions which might operate to limit Guarantor’s liability under, or the enforcement of, this Guaranty; or

(gg) to the fullest extent permitted by law, any other legal, equitable or surety defenses whatsoever to which Guarantor might otherwise be entitled, it being the intention that the obligations of Guarantor hereunder are absolute, unconditional and irrevocable.

Guarantor understands that the exercise by the Credit Parties of certain rights and remedies may affect or eliminate Guarantor’s right of subrogation against Borrower and that Guarantor may therefore incur partially or totally nonreimbursable liability hereunder. Nevertheless, Guarantor hereby authorizes and empowers the Credit Parties, their successors,

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endorsees and assigns, to exercise in its or their sole discretion, any rights and remedies, or any combination thereof, which may then be available, including, without limitation, any remedies against Borrower with respect to the Notes, it being the purpose and intent of Guarantor that the obligations hereunder shall be absolute, continuing, independent and unconditional under any and all circumstances.

4. Guarantor hereby consents and agrees that the Credit Parties may at any time, and from time to time, without thereb