NAME & ADDRESS HERE You must use the 11-digit Virtual Control Number located in the box to attend the Annual Meeting virtually, to vote via Internet, or to request proxy materials. Important Notice Regarding the Internet Availability of Proxy Materials for the Annual Meeting of Shareholders to be held virtually onDecember 16, 2025 at 8:00 a.m., Pacific Time This communication is not a form of voting and presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The Notice, Proxy Statement and Annual Report on Form 10-K are available at https://web.viewproxy.com/qmco/2025 If you want to receive a paper or email copy of these documents,you must request one by following the instructions below on or before December 9, 2025 to facilitate timely delivery. There is no charge to you for requesting a copy. Important information regarding the Internet availability of the Company’s proxy materials, instructions for accessing your proxy materials and voting online, and instructions for requesting paper or e-mail copies of your proxy materials are outlined in this Notice. CONTROL NUMBER SHAREHOLDERS ARE CORDIALLY INVITED TO ATTEND THE ANNUAL MEETING. To the Shareholders of Quantum Corporation The 2025 Annual Meeting of Shareholders of Quantum Corporation will be held virtually on December 16, 2025 at 8:00 a.m., Pacific Time. As a Registered Holder, you may attend and vote your shares at the virtual Annual Meeting by registering athttps://web.viewproxy.com/qmco/2025 and using the Virtual Control Number above. Your registration must be received by 11:59 p.m., Eastern Time on December 15, 2025. On the day of the Annual Meeting, if you have properly registered, you may log in using the password you received via email in your registration confirmation and follow the instructions to vote your shares. Please have your Virtual Control Number with you during the Annual Meeting in order to vote. Further instructions on how to attend and vote during the Annual Meeting are contained in the Proxy Statement. The Board recommends a vote “FOR” each nominee in Proposal 1 and “FOR” Proposals 2, 3, 4, 5, 6, 7 and 8. Proposal 1: Election of seven directors to serve for a term expiring at the 2026 annual meeting of shareholders or until their successors are duly qualified and elected. ELECTION OF DIRECTORS: (1) Hugues Meyrath (2) Tony J. Blevins (3) James C. Clancy (4) John A. Fichthorn (5) Donald J. Jaworski (6) John R. Tracy (7) Yue Zhou (Emily) White Proposal 2: Approval of, for purposes of complying with Nasdaq listing rule 5635, the issuance of senior secured convertible notes, convertible into shares of common stock, in exchange for all outstanding term loans owed to Dialectic Technology SPV LLC. Proposal 3: Approval of, for purposes of complying with Nasdaq listing rule 5635, the issuance of senior secured convertible notes, convertible into shares of common stock, in exchange for any additional funds raised by Dialectic Technology SPV LLC at our request. Proposal 4: Approval of, for purposes of complying with Nasdaq listing rule 5635, the issuance of any shares of common stock to Dialectic Technology SPV LLC that may become issuable under its forbearance warrant as a result of certain anti-dilution adjustments thereunder. Proposal 5: Approval of an amendment and restatement of the QuantumCorporation 2023 Long-Term Incentive Plan to increase the number of shares of common stock reserved for issuance thereunder by 1,400,000 shares and remove the individual annual award limits for employees orconsultants. Proposal 6: Approval of the compensation of our named executive officers, on a non-binding advisory basis. Proposal 7: Ratification of the appointment of CohnReznick LLP as our independent registered public accounting firm for the year endingMarch 31, 2026. Proposal 8: Approval of the adjournment of the Annual Meeting to a later date, if necessary or appropriate. NOTE: In their discretion, the proxy holders named in the proxy cards solicited on behalf of the Company’s Board of Directors (and their substitutes) are authorized to vote upon and transact such otherbusiness as may properly come before the meeting and anyadjournments or postponements thereof, including, without limitation, procedural and other matters related to the conduct of the meeting (such as adjournment to a later time or place) and the election of a substitute or alternate nominee if any nominee named herein isunwilling or unable to, or for good cause will not, serve if elected.
