UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 10-Q/A

Amendment No. 1

QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2012

Commission File Number: 000-22071

OVERLAND STORAGE, INC.

(Exact name of registrant as specified in its charter)

(858) 571-5555

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site every Interactive Data file required to be submitted and posted pursuant to Rule 405 of Regulation S-T (Section 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined by Rule 12b-2 of the Act).    Yes  ¨    No  x

As of November 2, 2012, there were 28,290,101 shares of the registrant’s common stock, no par value, issued and outstanding.

Explanatory Note

The purpose of this Amendment No. 1 to the Quarterly Report on Form 10-Q for Overland Storage, Inc. (the “Company”) for the period ended September 30, 2012, filed with the Securities and Exchange Commission on November 14, 2012 (the “Form 10-Q”), is to: correct the reference to an incorrect period that appeared in Part I, Item 4 “Controls and Procedures” to the Form 10-Q and (ii) provide additional information regarding disclosure that appeared in Part II, Item 5 “Other Information.” This Amendment No. 1 only affects Part I, Item 4 “Controls and Procedures” and Part II, Item 5 “Other Information” of the Form 10-Q and does not otherwise change or update the disclosures or financial information set forth in the Form 10-Q as originally filed and does not otherwise reflect events occurring after the original filing of the Form 10-Q.

PART I — FINANCIAL INFORMATION

Item 4. — Controls and Procedures

Disclosure Controls and Procedures

Under the supervision and with the participation of our management, including our principal executive officer and principal financial officer, we conducted an evaluation of our disclosure controls and procedures, as such term is defined under Rules 13a-15(e) and 15d-15(e) under the Exchange Act of 1934. Based on this evaluation, our principal executive officer and our principal financial officer concluded that our disclosure controls and procedures were effective as of the end of the period covered by this report.

Changes in Internal Control over Financial Reporting

There were no changes in our internal control over financial reporting during the fiscal quarter ended September 30, 2012 that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

PART II — OTHER INFORMATION

Item 5. — Other Information

On November 9, 2012, Shmuel Shottan resigned from our Board of Directors. Mr. Shottan did not advise us of any disagreement on any matter relating to our operations, policies or practices. On November 13, 2012, our Board of Directors, upon the recommendation of our Nominating and Governance Committee, appointed Vivekanand Mahadevan to fill one of the vacancies on our Board of Directors. In addition, Mr. Mahadevan was appointed to the Audit Committee of our Board of Directors. Mr. Mahadevan will serve on our Board of Directors for a term of office expiring at our next Annual Meeting of Shareholders. Mr. Mahadevan will receive compensation in accordance with our standard compensation arrangements for non-employee directors, which are described under the heading “Overview of Non-Employee Director Compensation and Procedures” in Item 11 of Part III of our Form 10-K for the fiscal year ended July 1, 2012, as filed with the Securities and Exchange Commission on September 13, 2012.

The Board of Directors has determined that Mr. Mahadevan qualifies as independent within the meaning of Rule 10A-3(b) of the Securities Exchange Act of 1934 and the independence standards set forth in NASDAQ Listing Rule 5605(a)(2).

Item 6. — Exhibits

SIGNATURE

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