UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (date of earliest event reported): November 4, 2013 (November 1, 2013)

OVERLAND STORAGE, INC.

(Exact name of registrant as specified in its charter)

9112 Spectrum Center Boulevard, San Diego, California 92123

(Address of principal executive offices, including zip code)

(858) 571-5555

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On November 1, 2013, Overland Storage, Inc., a California corporation (the “Company”), entered into an Acquisition Agreement (the “Acquisition Agreement”) with Tandberg Data Holdings S.à r.l., a private limited liability company (société à responsabilité limitée) incorporated under the laws of the Grand Duchy of Luxembourg (“Tandberg”) and Tandberg shareholders FBC Holdings S.à r.l. and Tandberg Data Management S.à r.l (collectively, “Tandberg Shareholders”). The Acquisition Agreement contemplates a series of transactions pursuant to which the Company will acquire from the Tandberg Shareholders all of the capital stock of Tandberg (the “Acquisition”). If the Acquisition is completed, Tandberg will become a wholly-owned subsidiary of the Company.

In connection with the Acquisition, the Company conducted an investor conference call on November 1, 2013 at 4:30 p.m. ET (1:30 p.m. PT) to discuss the Acquisition. A transcript of the conference call is furnished as Exhibit 99.1 hereto (the “Transcript”).

The Transcript is furnished and not filed pursuant to Item 7.01 as Exhibit 99.1 hereto. Such information shall not be deemed to be “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, and shall not be deemed to be incorporated by reference into any of the Company’s filings under the Securities Act or the Exchange Act whether made before or after the date hereof and regardless of any general incorporation language in such filings, except to the extent expressly set forth by specific reference in such a filing.

Important Additional Information About this Transaction

This communication may be deemed to be solicitation material in respect of the proposed acquisition of Tandberg by Overland and the associated issuance of shares of common stock in connection therewith. In connection with the proposed acquisition, the Company filed a form 8-K on November 1, 2013 describing the proposed acquisition, and intends to file additional relevant materials with the SEC, including Overland’s proxy statement on Schedule 14A. STOCKHOLDERS OF OVERLAND ARE URGED TO READ ALL RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING OVERLAND’S PROXY STATEMENT, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain the documents free of charge at the SEC’s web site, http://www.sec.gov, and Overland’s stockholders will receive information at an appropriate time on how to obtain transaction-related documents for free from Overland. Such documents are not currently available.

The Company and its directors and executive officers, Tandberg and its directors and executive officers, and Cyrus Capital Partners, L.P. and its directors and executive officers and certain of its affiliates may be deemed to be participants in the solicitation of proxies from the holders of common stock of the Company in respect of the proposed transaction. Information about the directors and executive officers of the Company is set forth in the proxy statement for the Company’s Annual Meeting of Shareholders held on June 18, 2013, which was filed with the Commission on May 17, 2013. Investors may obtain additional information regarding the interest of such participants by reading the proxy statement regarding the acquisition when it becomes available.

This document shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act.

Safe Harbor Statement

This Current Report on Form 8-K contains forward-looking statements that involve risks, uncertainties, and assumptions that are difficult to predict. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of risks and uncertainties including, without limitation, unforeseen changes in the course of the Company’s business or Tandberg’s business; any increase in the Company’s cash needs; possible actions by customers, suppliers, competitors or regulatory authorities with respect to the Company or Tandberg; and other risks detailed from time to time in the Company’s periodic reports filed with the Commission. The Company undertakes no obligation to update any forward-looking statement, whether written or oral, that may be made from time to time, whether as a result of new information, future developments or otherwise.

Please see the disclosure set forth under “Item 7.01 Regulation FD Disclosure”, which is incorporated by reference into this Item 8.01.

The Transcript is furnished and not filed pursuant to Item 8.01 as Exhibit 99.1 hereto. Such information shall not be deemed to be “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liabilities of that section, and shall not be deemed to be incorporated by reference into any of the Company’s filings under the Securities Act or the Exchange Act whether made before or after the date hereof and regardless of any general incorporation language in such filings, except to the extent expressly set forth by specific reference in such a filing.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report on Form 8-K to be signed on its behalf by the undersigned hereunto duly authorized.

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