DTLK Datalink Corp.

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS
TO BE HELD ON JANUARY 5, 2017

        NOTICE IS HEREBY GIVEN that a special meeting of the shareholders of Datalink Corporation, a Minnesota corporation (which we refer to as "Datalink," the "Company," "we," "our" or "us"), will be held at our principal executive offices, located at 10050 Crosstown Circle, Suite 500, Eden Prairie, Minnesota, on Thursday, January 5, 2017 at 9:00 a.m. local time (the "special meeting"), to consider and vote upon the following proposals:

1.

To approve and adopt the Agreement and Plan of Merger, dated as of November 6, 2016 (which, as it may be amended from time to time, we refer to as the "merger agreement"), by and among Datalink, Insight Enterprises, Inc., a Delaware corporation ("Insight"), and Reef Acquisition Co., a Minnesota corporation and a direct, wholly owned subsidiary of Insight ("Merger Sub"), pursuant to which Merger Sub will be merged with and into Datalink (the "merger");



2.

To approve, on an advisory (non-binding) basis, certain compensation that may be paid or become payable to Datalink's named executive officers in connection with the merger; and



3.

To approve the adjournment of the special meeting, if necessary or appropriate, including to solicit additional proxies if there are insufficient votes at the time of the special meeting to approve the proposal to adopt the merger agreement or in the absence of a quorum.

        Only shareholders of record as of the close of business on November 23, 2016 are entitled to notice of and to vote at the special meeting and at any adjournment or postponement thereof.

        Our board unanimously recommends that our shareholders vote (1) " FOR " the proposal to approve and adopt the merger agreement, (2) " FOR " the advisory (non-binding) proposal to approve certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger, and (3) " FOR " the proposal to adjourn the special meeting, if necessary or appropriate, including to solicit additional proxies or in the absence of a quorum.

        Your vote is important, regardless of the number of shares of our common stock you own. Regardless of whether you plan to attend the special meeting in person, we request that you complete, sign, date and return the enclosed proxy or submit your proxy by telephone or the internet prior to the special meeting to ensure that your shares will be represented at the special meeting. If you have internet access, we encourage you to submit your proxy via the internet. If you attend the special meeting, you may revoke your proxy and vote in person if you wish, even if you have previously returned your proxy card. Before voting your shares, we urge you to read the accompanying proxy statement carefully, including its annexes and the documents incorporated by reference in the document. Your prompt attention is greatly appreciated.

Minneapolis, Minnesota
November 29, 2016

Table of Contents

YOUR VOTE IS IMPORTANT

        If your shares are registered directly in your name:     If you are a shareholder of record, you may vote your shares through the internet, by telephone or by mail as described below. Please help us save time and postage costs by voting through the internet or by telephone. Each method is generally available 24 hours a day and will ensure that your vote is confirmed and posted immediately. To vote:

1.     BY INTERNET

a.

Go to the website at www.proxyvote.com , 24 hours a day, seven days a week, until 11:59 p.m., Eastern Time on January 4, 2017.



b.

Please have your proxy card available to verify your identity and create an electronic ballot.



c.

Follow the simple instructions provided.

2.     BY TELEPHONE

a.

On a touch-tone telephone in the United States, call toll-free 1 (800) 690-6903, 24 hours a day, seven days a week, until 11:59 p.m., Eastern Time on January 4, 2017.



b.

Please have your proxy card available to verify your identity.



c.

Follow the simple instructions provided.

3.     BY MAIL

a.

Mark, sign and date your proxy card.



b.

Return it in the postage-paid envelope that will be provided.

        If your shares are held in the name of a broker, bank or other nominee:     You should receive voting instructions from the organization holding your account and you must follow those instructions to vote your shares. As a beneficial owner, you have the right to direct your broker, bank or other nominee on how to vote the shares in your account. Your broker, bank or other nominee cannot vote on any of the proposals, including the proposal to approve and adopt the merger agreement, without your instructions.

        If you fail to return your proxy card, grant your proxy electronically over the internet or by telephone or vote by ballot in person at the special meeting, your shares will not be counted for purposes of determining whether a quorum is present at the special meeting. If you hold your shares through a broker, bank or other nominee, you must obtain from the record holder a valid legal proxy issued in your name in order to vote in person at the special meeting. A shareholder providing a proxy may revoke it at any time before it is exercised by providing written notice of revocation to our Secretary or by providing a proxy of a later date.

         You should not return your stock certificate or send documents representing our common stock with the proxy card. If the merger is completed, the paying agent for the merger will send you a letter of transmittal and related materials and instructions for exchanging your shares of our common stock for the merger consideration.

i

Table of Contents

        We encourage you to read the accompanying proxy statement, including all documents incorporated by reference into the accompanying proxy statement, and its annexes carefully and in their entirety. If you have any questions concerning the merger, the special meeting or the accompanying proxy statement, would like additional copies of the accompanying proxy statement or need help voting your shares of common stock, please contact our proxy solicitor:

If you have questions or need assistance voting your shares please contact:

105 Madison Avenue
New York, New York 10016
proxy@mackenziepartners.com
Call Collect: (212) 929-5500
or
Toll-Free 1 (800) 322-2885

ii

Table of Contents

TABLE OF CONTENTS

iii

Table of Contents

iv

Table of Contents

1

Table of Contents

2

Table of Contents

3

Table of Contents

4

Table of Contents

5

Table of Contents

6

Table of Contents

7

Table of Contents

8

Table of Contents

9

Table of Contents

QUESTIONS AND ANSWERS ABOUT THE SPECIAL MEETING AND THE MERGER

         The following questions and answers address briefly some questions you may have regarding the special meeting and the proposals to be voted on at the special meeting. These questions and answers may not address all of the questions that may be important to you as a shareholder of Datalink. Please refer to the more detailed information contained elsewhere in this document, the annexes to this document and the documents referred to or incorporated by reference in this document, which we urge you to read carefully and in their entirety. You may obtain the information incorporated by reference into this document without charge by following the instructions under the section entitled "Where You Can Find Additional Information" on page 89.

Q:

Why am I receiving this document?

A:

On November 6, 2016, Datalink entered into a definitive agreement providing for the merger of Merger Sub, a wholly owned subsidiary of Insight, with and into Datalink, with Datalink surviving the merger as a wholly owned subsidiary of Insight. You are receiving this document in connection with the solicitation of proxies by our board in favor of the proposal to approve and adopt the merger agreement and a proposal to adjourn the meeting, if necessary or appropriate, and to approve the other related proposal to be voted on at the special meeting.

Q:

What is a proxy?

A:

A proxy is your legal designation of another person, referred to as a "proxy," to vote your shares of our common stock. The written document describing the matters to be considered and voted on at the special meeting is called a "proxy statement." The document used to designate a proxy to vote your shares of our common stock is called a "proxy card." Our board has designated Gregory T. Barnum and Paul F. Lidsky, and each of them with full power of substitution, as proxies for the special meeting.

Q:

When and where is the special meeting?

A:

The special meeting will be held at Datalink's principal executive offices located at 10050 Crosstown Circle, Suite 500, Eden Prairie, MN 55344, on Thursday, January 5, 2017, at 9:00 a.m. local time (including any adjournment or postponement thereof, the "special meeting").

Q:

Who is entitled to vote at the special meeting?

A:

Only holders of record of our common stock as of the close of business on November 23, 2016, the record date for the special meeting, are entitled to receive these proxy materials and to vote their shares at the special meeting. As of the close of business on the record date, there were 22,256,459 shares of our common stock outstanding and entitled to vote at the special meeting, held by 158 holders of record. Each share of our common stock issued and outstanding as of the record date will be entitled to one vote on each matter submitted to a vote at the special meeting.

Q:

What is the difference between holding shares as a shareholder of record and as a beneficial owner?

A:

If your shares are registered directly in your name with our transfer agent, Wells Fargo Shareowner Services, you are considered, with respect to those shares, to be the "shareholder of record." In this case, we have sent this proxy statement and your proxy card to you directly.

If your shares are held through a broker, bank or other nominee, you are considered the "beneficial owner" of the shares of our common stock held in "street name." In that case, this proxy statement has been forwarded to you by your broker, bank or other nominee who is

10

Table of Contents

considered, with respect to those shares, to be the shareholder of record. As the beneficial owner, you have the right to direct your broker, bank or other nominee on how to vote your shares by following their instructions for voting. You are also invited to attend the special meeting. However, because you are not the shareholder of record, you may not vote your shares in person at the special meeting unless you request and obtain a valid legal proxy from your broker, bank or other nominee.

Q:

What matters will be voted on at the special meeting?

A:

You will be asked to consider and vote on the following proposals:

•

to approve and adopt the merger agreement;

•

to approve, on an advisory (non-binding) basis, certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger; and

•

to approve the adjournment of the special meeting, if necessary or appropriate, including to solicit additional proxies if there are insufficient votes at the time of the special meeting to approve the proposal to approve the merger agreement or in the absence of a quorum.

Q:

What is the proposed merger and what effects will it have on Datalink?

A:

The proposed merger is the acquisition of Datalink by Insight pursuant to the merger agreement. If the proposal to approve and adopt the merger agreement is approved by the holders of our common stock and the other closing conditions under the merger agreement have been satisfied or waived, Merger Sub will merge with and into Datalink, with Datalink continuing as the surviving corporation. As a result of the merger, Datalink will become a wholly owned subsidiary of Insight. We will cooperate with Insight to de-list our common stock from Nasdaq and de-register under the Exchange Act as soon as reasonably practicable following the effective time of the merger, and at such time, we will no longer be a publicly traded company and will no longer file periodic reports with the SEC. If the merger is consummated, you will not own any shares of the capital stock of the surviving corporation.

Q:

What happens if the merger is not completed?

A:

If the merger agreement is not approved by our shareholders or if the merger is not consummated for any other reason, our shareholders will not receive any payment for their shares of common stock. Instead, we will remain a public company, the common stock will continue to be listed and traded on Nasdaq and registered under the Exchange Act and we will continue to file periodic reports with the SEC.

Under specified circumstances, we may be required to pay Insight a termination fee upon the termination of the merger agreement, as described under " The Merger Agreement—Termination Fee " beginning on page 76.

Q:

What will I receive if the merger is completed?

A:

Upon completion of the merger, you will be entitled to receive the per-share merger consideration of $11.25 in cash, without interest and less any applicable withholding taxes, for each share of common stock that you own. For example, if you own 100 shares of common stock, you will receive $1,125.00 in cash in exchange for your shares of common stock, less any applicable withholding taxes. In any case, you will not own shares in the surviving corporation.

11

Table of Contents

Q:

What will the holders of Datalink restricted stock, stock options, RSUs and PSUs receive in the merger?

A:

Restricted Stock . At the effective time, each share of restricted stock that is outstanding immediately prior to the effective time will terminate and be cancelled in exchange for the merger consideration.

Stock Options. At the effective time, each stock option that is outstanding prior to the effective time, whether vested or unvested, will, (i) if the exercise price of such option is equal to or greater than the merger consideration, terminate and be cancelled without any consideration being payable; or (ii) if the exercise price of such option is less than the merger consideration, terminate and be cancelled in exchange for the aggregate option consideration with respect to such option. The option consideration equals the difference between the merger consideration and the exercise price payable for each share issuable under such option.

Restricted Stock Units and Performance Stock Units. At the effective time, each award of Datalink RSUs or PSUs that is outstanding or payable prior to the effective time, whether vested or unvested, will terminate and be cancelled as of immediately prior to the effective time in exchange for the right to receive the product of (i) the number of shares subject to such RSU or PSU, as applicable; and (ii) the merger consideration (subject to any applicable withholding tax). For purposes of the merger agreement, the deferred stock units held by certain of our directors are considered RSUs.

Q:

When do you expect the merger to be completed?

A:

We are working toward completing the merger as soon as possible on or after the date of the special meeting, and currently expect to consummate the merger during the first quarter of 2017. However, the exact timing of completion of the merger cannot be predicted because the merger is subject to conditions, including approval of the merger agreement by our shareholders and the receipt of regulatory approvals. See " The Merger Agreement—When the Merger Becomes Effective " on page 62 and " The Merger Agreement—Conditions to Completion of the Merger " beginning on page 73.

Q:

Am I entitled to appraisal or dissenters' rights under Minnesota Law?

A:

Yes. As a holder of the Company's common stock, you are entitled to exercise dissenters' rights under the Minnesota Business Corporation Act in connection with the merger if you take certain actions and meet certain conditions. See " Dissenters' Rights " beginning on page 85.

Q:

Will I be subject to U.S. federal income tax upon the exchange of our common stock for cash pursuant to the merger?

A:

If you are a U.S. holder (as defined under " The Merger (Proposal 1)—Material U.S. Federal Income Tax Consequences of the Merger " beginning on page 57), the exchange of our common stock for cash pursuant to the merger generally will require a U.S. holder to recognize a gain or loss for U.S. federal income tax purposes in an amount equal to the difference between the amount of cash received by such U.S. holder pursuant to the merger and such U.S. holder's adjusted tax basis in the shares of our common stock surrendered pursuant to the merger. Backup withholding may also apply to the cash payment pursuant to the merger unless the U.S. holder or other payee provides a taxpayer identification number, certifies that such number is correct and otherwise complies with the backup withholding rules. Because particular circumstances may differ, we recommend that you consult your own tax advisor to determine the U.S. federal income tax consequences relating to the merger in light of your own particular circumstances and any consequences arising under the laws of any state, local or foreign taxing jurisdiction. A more

12

Table of Contents

complete description of the U.S. federal income tax consequences of the merger is provided under " The Merger (Proposal 1)—Material U.S. Federal Income Tax Consequences of the Merger " beginning on page 57 of this proxy statement.

Q:

How do I attend the special meeting?

A:

To attend the meeting, you will need to present valid photo identification, such as a driver's license or passport, and proof of ownership of our common stock. If your shares are held in the name of a broker, bank or other nominee, you will need to present a recent brokerage statement or letter from such entity reflecting your stock ownership as of the record date. If you do not provide photo identification or comply with the other procedures outlined in this document, you will not be admitted to the special meeting. For security reasons, you and your bags may be subject to search prior to your admittance to the meeting.

If you are not a holder of record as of the record date, you may be admitted to the meeting only if you have a valid legal proxy from a holder of record as of the record date. You must present that proxy, as well as a form of valid photo identification, at the entrance to the meeting.

Q:

How many shares are needed to constitute a quorum?

A:

A quorum will be present if holders of record of a majority of the shares of our common stock outstanding on the close of business on the record date are present in person or represented by proxy at the special meeting. If a quorum is not present at the special meeting, the special meeting may be adjourned or postponed from time to time until a quorum is obtained.

If you submit a proxy but fail to provide voting instructions or abstain on any of the proposals listed on the proxy card, your shares will be counted for the purpose of determining whether a quorum is present at the special meeting.

If your shares are held in "street name" by your broker, bank or other nominee and you do not instruct the nominee how to vote your shares, your broker, bank or other nominee will not vote on your behalf with respect to any of the proposals, and your shares will not be counted for purposes of determining whether a quorum is present for the transaction of business at the special meeting.

Q:

What vote of Datalink shareholders is required to approve and adopt the merger agreement?

A:

Approval of the merger agreement requires that shareholders holding a majority of the shares of our common stock outstanding at the close of business on the record date for the special meeting and entitled to be cast on such proposal vote "FOR" the proposal to approve and adopt the merger agreement. A failure to vote your shares of our common stock or an abstention from voting will have the same effect as a vote "AGAINST " the proposal to approve and adopt the merger agreement. If your shares are held in "street name" by your broker, bank or other nominee and you do not instruct the nominee how to vote your shares, such failure to instruct your nominee will have the same effect as a vote "AGAINST" the proposal to approve and adopt the merger agreement.

Q:

What vote of Datalink shareholders is required to approve the other proposals to be voted upon at the special meeting?

A:

Each of the advisory (non-binding) proposal to approve certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger and the proposal to adjourn the special meeting, if necessary or appropriate, including to solicit additional proxies or in the absence of a quorum, requires that more shares are voted "FOR" such proposal than "AGAINST."

13

Table of Contents

An abstention with respect to either proposal and a failure to vote your shares of our common stock on either proposal (including a failure of your broker, bank or other nominee to vote shares held on your behalf), assuming a quorum is present, will not have the effect of either a vote "FOR" or a vote "AGAINST" such proposals.

Q:

How does our board recommend that I vote?

A:

Our board unanimously recommends that our shareholders vote:

•

" FOR " the proposal to approve and adopt the merger agreement;

•

" FOR " the advisory (non-binding) proposal to approve certain compensation that may be paid or become payable to our named executive officers in connection with the merger; and

•

" FOR " the proposal regarding adjournment of the special meeting.

For a discussion of the factors that our board considered in determining to recommend the approval of the merger agreement, please see the section entitled " The Merger (Proposal 1)—Reasons for our Board's Recommendation in Favor of the Merger " beginning on page 35. In addition, in considering the recommendation of our board with respect to the merger agreement, you should be aware that some of our directors and executive officers have potential interests that may be different from, or in addition to, the interests of our shareholders generally. For a discussion of these interests, please see the section entitled " The Merger (Proposal 1)—Interests of Datalink's Directors and Executive Officers in the Merger " beginning on page 48.

Q:

How do Datalink's directors and officers intend to vote?

A:

Each of our directors has agreed with Insight that they will vote their shares in favor of the proposal to approve and adopt the merger agreement and a proposal to adjourn the meeting, if necessary or appropriate, and we expect the directors to also vote their shares in favor of the other proposal to be considered at the special meeting. See " The Voting Agreement " beginning on page 78. We currently expect that our executive officers will also vote their shares in favor of the proposal to approve and adopt the merger agreement and the other proposals to be considered at the special meeting, although they have no obligation to do so.

Q:

What will happen if shareholders do not approve the advisory (non-binding) proposal on certain compensation that may be paid or become payable to Datalink's named executive officers in connection with the merger?

A:

The inclusion of this proposal is required by the SEC rules; however, the approval of this proposal is not a condition to the completion of the merger and the vote on this proposal is an advisory vote by shareholders and is not binding on Datalink or Insight. If the merger agreement is approved by Datalink shareholders and the merger is completed, the merger-related compensation will be paid to Datalink's named executive officers in accordance with the terms of their compensation agreements and arrangements even if shareholders do not approve this proposal.

Q:

What do I need to do now? How do I vote my shares of our common stock?

A:

We urge you to read this entire document carefully, including its annexes and the documents incorporated by reference, and to consider how the merger affects you. Your vote is important, regardless of the number of shares of our common stock you own. See page i at the beginning of this proxy statement for instructions on how to vote your shares in person or by proxy over the internet, by telephone or by mail.

14

Table of Contents

Q:

Can I revoke my proxy?

A:

Yes. You may revoke your proxy and change your vote at any time before your proxy is voted at the annual meeting. To revoke your proxy, you must (a) submit a new proxy with a more recent date than that of the first proxy given before 11:59 P.M. Eastern Time on January 4, 2017 by (1) following the Internet voting instructions or (2) following the telephone voting instructions; (b) complete, sign, date and return a new proxy card to us, which must be received by us before the time of the meeting; or (c) if you are a registered shareholder, attend the meeting in person and deliver a proper written notice of revocation of your proxy. Attendance at the meeting will not by itself revoke a previously granted proxy. Unless you decide to vote your shares in person, you should revoke your prior proxy in the same way you initially submitted it—that is, by Internet, telephone or mail.

Q:

Will my shares of our common stock held in "street name" or another form of record ownership be combined for voting purposes with shares I hold of record?

A:

No. Because any shares of our common stock you may hold in "street name" will be deemed to be held by a different shareholder (that is, your custodial bank, broker or other financial nominee) than any shares of our common stock you hold of record, any shares of our common stock held in "street name" will not be combined for voting purposes with shares of our common stock you hold of record. Similarly, if you own shares of our common stock in various registered forms, such as jointly with your spouse, as trustee of a trust or as custodian for a minor, you will receive, and will need to sign and return, a separate proxy card for those shares of our common stock because they are held in a different form of record ownership. Shares of our common stock held by a corporation or business entity must be voted by an authorized officer of the entity. Please indicate title or authority when completing and signing the proxy card. Shares of our common stock held in an individual retirement account must be voted under the rules governing the account. This means that, to ensure all your shares are voted at the special meeting, you should read carefully any proxy materials received and follow the instructions included therewith.

Q:

What does it mean if I get more than one proxy card or voting instruction card?

A:

If your shares of our common stock are registered differently or are held in more than one account, you will receive more than one proxy or voting instruction card. Please complete and return all of the proxy cards and voting instruction cards you receive (or submit each of your proxies by telephone or the internet, if available to you) to ensure that all of your shares of our common stock are voted.

Q:

What happens if I sell my shares of our common stock before completion of the merger?

A:

In order to receive the merger consideration, you must hold your shares of our common stock through completion of the merger. Consequently, if you transfer your shares of our common stock before completion of the merger, you will have transferred your right to receive the merger consideration in the merger.

The record date for shareholders entitled to vote at the special meeting is earlier than the consummation of the merger. If you transfer your shares of our common stock after the record date but before the closing of the merger, you will have the right to vote at the special meeting but not the right to receive the merger consideration.

Q:

Should I send in my stock certificates or other evidence of ownership now?

A:

No. After the merger is completed, you will receive a letter of transmittal and related materials from the paying agent for the merger with detailed written instructions for exchanging your shares

15

Table of Contents

of our common stock evidenced by stock certificates for the merger consideration. If your shares of our common stock are held in "street name" by your broker, bank or other nominee, you may receive instructions from your broker, bank or other nominee as to what action, if any, you need to take to effect the surrender of your "street name" shares in exchange for the merger consideration. Do not send in your certificates now.

Q:

Where can I find the voting results of the special meeting?

A:

We intend to announce preliminary voting results at the special meeting and publish final results in a Current Report on Form 8-K that will be filed with the SEC following the special meeting. All reports that we file with the SEC are publicly available when filed. See " Where You Can Find Additional Information " on page 89 of this proxy statement.

Q:

Where can I find more information about Datalink?

A:

You can find more information about us from various sources described in the section entitled " Where You Can Find Additional Information " on page 89.

Q:

Who can help answer my other questions?

A:

If you have more questions about the merger, or require assistance in submitting your proxy or voting your shares or need additional copies of this document or the enclosed proxy card, please contact MacKenzie Partners, Inc., which is acting as the proxy solicitation agent and information agent for Datalink in connection with the merger.

If you have questions or need assistance voting your shares, please contact:

105 Madison Avenue
New York, New York 10016
proxy@mackenziepartners.com
Call Collect: (212) 929-5500
or
Toll-Free 1 (800) 322-2885

or

Datalink Corporation
Attn: Investor Relations
10050 Crosstown Circle, Suite 500
Eden Prairie, Minnesota 55344
(952) 944-3462

        If your broker, bank or other nominee holds your shares, you should also call your broker, bank or other nominee for additional information.

16

Table of Contents

CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING STATEMENTS

        The Private Securities Litigation Reform Act of 1995 provides a "safe harbor" for certain forward-looking statements. This communication contains forward-looking statements, including statements relating to the completion of the transaction and statements regarding Datalink's future performance. Forward-looking statements can usually be identified by the use of words such as "aim," "anticipate," "believe," "continue," "could," "estimate," "evolve," "expect," "forecast," "intend," "looking ahead," "may," "opinion," "plan," "possible," "potential," "project," "should," "will" and other expressions which indicate future events or trends. Forward-looking statements are likely to address matters such as, among other things, Datalink's, Insight's and their respective affiliates' respective or combined anticipated sales, expenses, margins, tax rates, capital expenditures, profits, cash flows, liquidity and debt levels. These forward-looking statements are based on the companies' current plans, expectations and assumptions and involve a number of risks and uncertainties that could cause actual results and events to vary materially from the results and events anticipated or implied by such forward-looking statements.

        These risks and uncertainties include, but are not limited to, the following factors:

•

the risk that we are unable to consummate the merger within the anticipated time period, or at all, due to the failure to obtain shareholder approval to approve and adopt the merger agreement or failure to satisfy the other conditions to the completion of the merger;



•

the risk that the merger agreement may be terminated in circumstances requiring us to pay Insight a termination fee of $7.5 million;



•

the risk of any event, change or other circumstances occurring that could give rise to the termination of the merger agreement;



•

the risk that Insight may be unable to access its financing or the failure of any such financing to be sufficient to consummate the merger and the other transactions contemplated by the merger agreement;



•

the risks that the proposed merger disrupts our current plans and operations or affects our ability to retain or recruit key employees;



•

the effect of the announcement or pendency of the merger on our business relationships (including, without limitation, customers and suppliers), operating results and business generally;



•

the amount of the costs, fees, expenses and charges related to the merger agreement or the merger;



•

the risks related to diverting management's or employees' attention from ongoing business operations;



•

the risks associated with limitations placed on our ability to operate our business under the merger agreement;



•

the risk that our stock price may decline significantly if the merger is not completed or may suffer as a result of uncertainty surrounding the merger;



•

the risk that the merger may not be consummated in a timely manner, if at all;



•

the nature, cost and outcome of pending and future litigation and other legal proceedings, including any such proceedings related to the merger and instituted against us and others;



•

the possibility that the companies may be adversely affected by other economic, business and/or competitive factors;



•

worldwide economic conditions and their impact on customer purchasing decisions;

17

Table of Contents

•

rapid technological changes and competitive pressures in the industry; and



•

the other risks, factors and matters described or incorporated by reference in this proxy statement, including the "Risk Factors" described in our Form 10-K for the fiscal year ended December 31, 2015 and in our subsequent filings on Form 10-Q (see " Where You Can Find Additional Information " on page 89).

        Many of these factors are beyond our ability to control or predict. In light of the significant uncertainties inherent in the forward-looking statements contained herein, readers should not place undue reliance on forward-looking statements, which speak only as of the date hereof. We cannot guarantee any future results, levels of activity, performance or achievements. Except as required by applicable law, we undertake no obligation to update forward-looking statements to reflect events or circumstances arising after such date.

18

Table of Contents

THE COMPANIES

Datalink

        Datalink Corporation, referred to as "Datalink," the "Company," "we," "our" or "us," is a Minnesota corporation. Datalink was incorporated in Minnesota in 1987. We provide information technology (IT) services and solutions that help organizations transform technology, operations and service delivery to meet business challenges. Focused on midsize and large companies, we provide a full life cycle of services including consulting, strategy, design, deployment, management, and support. We leverage technology from the industry's leading original equipment manufacturers (OEMs) as part of our IT solutions portfolio.

        Our solutions can include hardware products, such as servers, disk arrays, tape systems, networking and interconnection components and software products. Our data center strategy is supported through multiple trends in the market and involves supporting the market and our clients with a single vendor to provide their data center infrastructure needs. As of September 30, 2016, we had 36 locations, including both leased facilities and home offices, throughout the United States. We historically have derived our greatest percentage of net sales from clients located in the central part of the United States.

        Our common stock is currently listed on the Nasdaq Global Market under the ticker symbol "DTLK."

        Our principal executive offices are located at 10050 Crosstown Circle, Suite 500, Eden Prairie, Minnesota 55344, and our telephone number is (952) 944-3462. Datalink's website is located at www.datalink.com . The information contained on, or accessible through, our website is not incorporated into, and does not form a part of, this proxy statement or any other report or document on file with or furnished to the SEC.

Insight

        Insight Enterprises, Inc., referred to as "Insight," is a Delaware corporation. The Company was incorporated in Delaware in 1991 and is the successor to a business that commenced operations in 1988. Insight is a Fortune 500-ranked global provider of IT hardware, software, cloud and service solutions to business, government, healthcare and educational clients in North America, Europe, the Middle East, Africa ("EMEA"), and Asia-Pacific ("APAC"). Insight's offerings in North America and select countries in EMEA include hardware, software and services. Its offerings in the remainder of its EMEA segment and in APAC are largely software and select software-related services.

        Insight's common stock is currently listed on the Nasdaq Global Select Market under the ticker symbol "NSIT."

        Insight's principal executive offices are located at 6820 South Harl Avenue, Tempe, Arizona 85283, and its telephone number is (480) 333-3000. Insight's website is located at www.insight.com . The information contained on, or accessible through, Insight's website is not incorporated into, and does not form a part of, this proxy statement or any other report or document on file with or furnished to the SEC.

Merger Sub

        Reef Acquisition Co., referred to as "Merger Sub," is a Minnesota corporation and a wholly owned subsidiary of Insight. Merger Sub was formed in November 2016 solely for the purpose of entering into the merger agreement and consummating the transactions contemplated by the merger agreement, and it currently has no other business or operations. Upon completion of the merger, Merger Sub will cease to exist and Datalink will continue as the surviving corporation.

        Merger Sub's principal executive offices are located at 6820 South Harl Avenue, Tempe, Arizona 85283, and its telephone number is (480) 333-3000.

19

Table of Contents

THE SPECIAL MEETING

         We are furnishing this document to Datalink shareholders as part of the solicitation of proxies by our board for use at the special meeting or any adjournment or postponement thereof. This document provides Datalink shareholders with the information they need to know to be able to vote or instruct their vote to be cast at the special meeting or any adjournment or postponement thereof.

Date, Time and Place of the Special Meeting

        This document is being furnished to our shareholders as part of the solicitation of proxies by our board for use at the special meeting to be held at Datalink's principal executive offices located at 10050 Crosstown Circle, Suite 500, Eden Prairie, Minnesota 55344, on Thursday, January 5, 2017 at 9:00 a.m. local time, or at any adjournment or postponement thereof.

        To attend the meeting, you will need to present valid photo identification, such as a driver's license or passport, and proof of ownership of our common stock. If your shares are held in the name of a broker, bank or other nominee, you will need to present a recent brokerage statement or letter from such entity reflecting your stock ownership as of the record date.

        If you are not a holder of record as of the record date, you may be admitted to the meeting only if you have a valid legal proxy from a holder of record as of the record date who has obtained an admission ticket. You must present that proxy and admission ticket, as well as a form of valid photo identification, at the entrance to the meeting.

Purposes of the Special Meeting

        At the special meeting, Datalink shareholders will be asked to consider and vote on the following proposals:

•

to approve and adopt the merger agreement, dated as of November 6, 2016, by and among Datalink, Insight and Merger Sub, a wholly owned subsidiary of Insight;



•

to approve, on an advisory (non-binding) basis, certain compensation that may be paid or become payable to Datalink's named executive officers in connection with the merger, the value of which is disclosed in the table in the section of this document entitled " The Merger (Proposal 1)—Interests of Datalink's Directors and Executive Officers in the Merger " beginning on page 48; and



•

to approve the adjournment of the special meeting, if necessary or appropriate, including to solicit additional proxies if there are insufficient votes at the time of the special meeting to approve the proposal to approve and adopt the merger agreement or in the absence of a quorum.

        Our shareholders must approve and adopt the merger agreement for the merger to occur. If our shareholders fail to approve and adopt the merger agreement, the merger will not occur. A copy of the merger agreement is attached to this document as Annex A , and the material provisions of the merger agreement are described in the section entitled " The Merger Agreement " beginning on page 61.

        The vote on executive compensation payable in connection with the merger is a vote separate and apart from the vote to approve and adopt the merger agreement. Accordingly, a shareholder may vote to approve the executive compensation and vote not to approve and adopt the merger agreement and vice versa. Because the vote on executive compensation is advisory in nature only, it will not be binding on either Datalink or Insight. Accordingly, if the merger agreement is approved by Datalink shareholders and the merger is completed, the merger-related compensation may be paid to Datalink's executive officers even if the shareholders fail to approve the proposal.

20

Table of Contents

        Datalink does not expect a vote to be taken on any other matters at the special meeting or any adjournment or postponement thereof. If any other matters are properly presented at the special meeting or any adjournment or postponement thereof for consideration, however, the holders of the proxies will have discretion to vote on these matters in accordance with their best judgment.

        This document and the enclosed form of proxy are first being mailed to Datalink shareholders on or about November 30, 2016.

Record Date and Quorum

        The holders of record of our common stock as of the close of business on November 23, 2016, the record date for the special meeting, are entitled to receive notice of and to vote at the special meeting. At the close of business on the record date, 22,256,459 shares of our common stock were outstanding.

        The presence at the special meeting, in person or represented by proxy, of the holders of record of a majority of our common stock outstanding at the close of business on the record date will constitute a quorum. Once a share is represented at the special meeting, it will be counted for the purpose of determining a quorum at the special meeting. However, if a new record date is set for an adjourned special meeting, then a new quorum will have to be established. Proxies received but marked as abstentions will be included in the calculation of the number of shares considered to be present at the special meeting.

Required Vote

        Each share of our common stock outstanding at the close of business on the record date is entitled to one vote on each of the proposals to be considered at the special meeting.

        For Datalink to complete the merger, Datalink shareholders holding a majority of the shares of our common stock outstanding at the close of business on the record date and entitled to vote on such proposal must vote "FOR" the proposal to approve and adopt the merger agreement. A failure to vote your shares of our common stock or an abstention from voting will have the same effect as a vote "AGAINST" the proposal to approve and adopt the merger agreement.

        Approval of each of the advisory (non-binding) proposal on certain compensation that may be paid or become payable to Datalink's named executive officers in connection with the merger and the adjournment proposal requires that more shares are voted "FOR" than "AGAINST" such proposal. An abstention with respect to either proposal and a failure to vote your shares of our common stock (including a failure of your broker, bank or other nominee to vote shares held on your behalf), assuming a quorum is present, will not have the effect of either a vote "FOR" or a vote "AGAINST" these proposals.

Voting by Datalink's Directors and Executive Officers

        At the close of business on the record date, our directors and executive officers were entitled to vote approximately 1,814,504 shares of our common stock, which in the aggregate represents approximately 8.2% of the shares of our common stock issued and outstanding on that date. Each of our directors has agreed with Insight that they will vote their shares in favor of the proposal to approve and adopt the merger agreement and a proposal to adjourn the meeting, if necessary or appropriate, and we expect the directors to also vote their shares in favor of the other proposal to be considered at the special meeting. See " The Voting Agreement " beginning on page 78. We currently expect that our executive officers will also vote their shares in favor of the proposal to approve and adopt the merger agreement and the other proposals to be considered at the special meeting, although they have no obligation to do so.

21

Table of Contents

        A total of 11,128,230 votes are needed to approve and adopt the merger agreement. Approximately 1,558,264 shares are held by our directors and subject to the voting agreement. Therefore, approximately 9,569,966 additional votes entitled to be cast by shareholders other than our directors must be cast to approve and adopt of the merger agreement in order to approve the transaction.

Voting; Proxies; Revocation

Attendance

        All holders of shares of our common stock as of the close of business on November 23, 2016, the record date, including shareholders of record and beneficial owners of our common stock registered in the "street name" of a broker, bank or other nominee, are invited to attend the special meeting. If you are a shareholder of record, please be prepared to provide valid photo identification, such as a driver's license or passport, and proof of ownership of our common stock. If your shares are held in the name of a broker, bank or other nominee, you will need to present a recent brokerage statement or letter from such entity reflecting your stock ownership as of the record date. If you do not provide photo identification or comply with the other procedures outlined in this document, you will not be admitted to the special meeting. For security reasons, you and your bags may be subject to search prior to your admittance to the meeting.

        If you are not a holder of record as of the record date, you may be admitted to the meeting only if you have a valid legal proxy from a holder of record as of the record date. You must present that proxy, as well as a form of valid photo identification, at the entrance to the meeting.

Voting in Person

        Shareholders of record will be able to vote in person at the special meeting. We will give you a ballot when you arrive. If you are not a shareholder of record but instead hold your shares of our common stock in "street name" through a broker, bank or other nominee, you must provide a legal proxy executed in your favor from your broker, bank or other nominee in order to be able to vote in person at the special meeting. Attending the meeting in person does not itself constitute a vote on any proposal.

Providing Voting Instructions by Proxy

        To ensure that your shares of our common stock are voted at the special meeting, we recommend that you provide voting instructions promptly by proxy, even if you plan to attend the special meeting in person.

Shares of Common Stock Held by Record Holder

        If you are a shareholder of record, you may provide voting instructions by proxy using one of the methods described below.

         To vote over the internet , go to the web address www.proxyvote.com and follow the instructions for voting. Have your proxy card available when you access the web page. If you vote over the internet, please do not mail your proxy card.

         To vote by telephone , dial 1 (800) 690-6903 in the United States from any touch-tone telephone and follow the instructions. Have your proxy card available when you call. If you vote by telephone, please do not mail your proxy card.

         To vote by mail , mark your proxy card, date and sign it and return it in the postage-prepaid envelope. You should not return your stock certificate or send documents representing our common

22

Table of Contents

stock with the proxy card. If the merger is completed, the paying agent for the merger will send you a letter of transmittal and related materials and instructions for exchanging your shares of our common stock for the merger consideration.

        If you vote by proxy (regardless of whether you vote over the internet, by telephone or by mail), your votes must be received by 11:59 p.m., Eastern Time, on January 4, 2017 to be counted.

        Your proxy card will count as a "vote" if you sign, date and return your proxy card without indicating how you wish to vote with respect to a proposal. In this case, your proxy will be voted "FOR" such proposal.

        A failure to vote or an abstention will have the same effect as voting "AGAINST" the proposal to approve and adopt the merger agreement. An abstention and, assuming a quorum is present, a failure to vote will not have the effect of either a vote "FOR" or a vote "AGAINST" on the other two proposals.

Shares of Common Stock Held in "Street Name"

        If you hold your shares in "street name" through a broker, bank or other nominee, you should follow the directions provided by your broker, bank or other nominee regarding how to instruct your broker, bank or other nominee to vote your shares. Without those instructions, your shares will not be voted on any of the proposals, which will have the same effect as voting "AGAINST" the proposal to approve and adopt the merger agreement, but, assuming a quorum is present, will not have the effect of either a vote "FOR" or a vote "AGAINST" the other two proposals.

        In accordance with the rules of Nasdaq, brokers, banks and other nominees that hold shares of our common stock in "street name" for their customers do not have discretionary authority to vote the shares with respect to the proposal to approve and adopt the merger agreement, the advisory (non-binding) proposal to approve certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger, or the adjournment of the special meeting, if necessary or appropriate, including to solicit additional proxies or in the absence of a quorum. Accordingly, if brokers, banks or other nominees do not receive specific voting instructions from the beneficial owner of such shares, they may not vote such shares with respect to these proposals. Therefore, unless you attend the special meeting in person with a properly executed legal proxy from your broker, bank or other nominee, your failure to provide instructions to your broker, bank or other nominee will result in your shares of our common stock not being present at the meeting and not being voted on any of the proposals. Consequently, there cannot be any broker non-votes occurring in connection with any of the proposals at the special meeting.

Revocation of Proxies

        Any person giving a proxy pursuant to this solicitation has the power to revoke and change it at any time before it is voted. If you are a shareholder of record, you may revoke your proxy by:

•

submitting a new proxy card with a later date, which is received by Datalink prior to the final vote at the special meeting;



•

using the telephone or internet proxy submission procedures described above, or by completing, signing, dating and returning a new proxy card by mail to Datalink;



•

attending the special meeting and voting in person; or



•

delivering a written notice of revocation by mail to Datalink in care of the Secretary at 10050 Crosstown Circle, Suite 500, Eden Prairie, MN 55344, Attn: Secretary, which is received by Datalink prior to the final vote at the special meeting.

23

Table of Contents

        Please note that only your last-dated proxy will count. Attending the special meeting without taking one of the actions described above will not in itself revoke your proxy. If you want to revoke your proxy by mailing a new proxy card to Datalink or by sending a written notice of revocation to Datalink, you should ensure that you send your new proxy card or written notice of revocation in sufficient time for it to be received by Datalink before the special meeting.

        Please note that if you hold your shares in "street name" and you have instructed a broker, bank or other nominee to vote your shares, you should instead follow the instructions received from your broker, bank or other nominee to revoke your prior voting instructions. If you hold your shares in "street name," you may also revoke a prior proxy by voting in person at the special meeting if you obtain a proxy executed in your favor from your broker, bank or other nominee in order to be able to vote in person at the special meeting.

Abstentions

        An abstention occurs when a shareholder attends a meeting, either in person or represented by proxy, but abstains from voting. Abstentions will be included in the calculation of the number of shares of our common stock present or represented at the special meeting for purposes of determining whether a quorum has been achieved.

        Abstaining from voting will have the same effect as a vote "AGAINST" the proposal to approve and adopt the merger agreement. The requisite number of shares to approve the other two proposals is based on the total number of shares voted "FOR" such proposal compared to the number of shares voted "AGAINST" such proposal. If you abstain from voting with respect to such proposals or do not vote on such proposals, such failure to vote will not have the effect of either a vote "FOR" or a vote "AGAINST" the advisory (non-binding) proposal on certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger or the proposal regarding adjournment of the special meeting.

Board of Directors' Recommendation

        Our board, after considering various factors described in the section entitled " The Merger (Proposal 1)—Reasons for our Board's Recommendation in Favor of the Merger " beginning on page 35, unanimously determined that the merger agreement and the transactions contemplated by the merger agreement, including the merger, are fair to, advisable and in the best interests of Datalink and our shareholders, and approved the merger agreement and the transactions contemplated by the merger agreement, including the merger.

        The Board unanimously recommends that you vote (1) " FOR " the proposal to approve and adopt the merger agreement, (2) " FOR " the advisory (non-binding) proposal to approve certain compensation that may be paid or become payable to the named executive officers of Datalink in connection with the merger, and (3) " FOR " the proposal to adjourn the special meeting, if necessary or appropriate, including to solicit additional proxies or in the absence of a quorum.

Solicitation of Proxies

        Our board is soliciting your proxy, and we will bear the cost of this solicitation of proxies. This includes the charges and expenses of brokerage firms and others for forwarding solicitation material to beneficial owners of our outstanding common stock. We have retained MacKenzie Partners, Inc. ("MacKenzie"), a proxy solicitation firm, to assist our board in the solicitation of proxies for the special meeting, and we expect to pay MacKenzie $12,500, plus reimbursement of out-of-pocket expenses. Proxies may be solicited by mail, personal interview, email, telephone, or via the internet by MacKenzie or, without additional compensation, by certain of our directors, officers and employees.

24

Table of Contents

Other Business

        We are not currently aware of any business to be acted upon at the special meeting other than the matters discussed in this proxy statement. Under our by-laws, business transacted at the special meeting is limited to matters relating to the purposes stated in the notice of the special meeting, which is provided at the beginning of this proxy statement. The grant of a proxy will confer discretionary authority on the persons named as proxies on the proxy card to vote in accordance with their best judgment on procedural matters incident to the conduct of the special meeting.

Notice Regarding the Availability of Proxy Materials for the Special Meeting to be Held on January 5, 2017

        The proxy statement is available at www.proxyvote.com .

25

Table of Contents