<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-02-18</periodOfReport>

    <issuer>
        <issuerCik>0000889930</issuerCik>
        <issuerName>OVERLAND STORAGE INC</issuerName>
        <issuerTradingSymbol>OVRL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001468579</rptOwnerCik>
            <rptOwnerName>Mansolf Jillian</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O OVERLAND STORAGE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>4820 OVERLAND AVENUE</rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP, WW Sales &amp; Marketing</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Series A Convertible Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.6362</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-02-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.00</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>22760</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrants</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.583</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-02-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>32080</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.00</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2010-02-22</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-02-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>32080</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>32080</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The Series A Preferred Stock is convertible (i) at the option of the holder at any time after the record date for the special meeting of shareholders to approve the issuance and sale of the Series A Preferred Stock and Warrants (including the shares of Common Stock issuable upon conversion of the Series A Preferred Stock and exercise of the Warrants) or (ii) automatically if the shareholders approve the issuance and sale of Series A Preferred Stock and Warrants (including the shares of Common Stock issuable upon conversion of the Series A Preferred Stock and exercise of the Warrants).</footnote>
        <footnote id="F2">Pursuant to the Certificate of Determination of Rights, Preferences, Privileges and Restrictions of Series A Convertible Preferred Stock dated February 18, 2010, a holder of shares of Series A Preferred Stock may not convert any such shares to the extent that after giving effect to such conversion the holder would beneficially own in excess of 19.999% of the total number of shares of common stock outstanding.  The limitation on conversion of shares of Series A Preferred Stock will terminate if the shareholders approve the issuance and sale of Series A Preferred Stock and Warrants (including the shares of Common Stock issuable upon conversion of the Series A Preferred Stock and exercise of the Warrants).</footnote>
        <footnote id="F3">No expiration date.</footnote>
        <footnote id="F4">Pursuant to the terms of the Warrants, no holder of Warrants may exercise any such Warrants to the extent that after giving effect to such exercise the holder would beneficially own in excess of 19.999% of the total number of shares of common stock outstanding.  The limitation on exercise of the Warrants will terminate if the shareholders approve the issuance and sale of Series A Preferred Stock and Warrants (including the shares of Common Stock issuable upon conversion of the Series A Preferred Stock and exercise of the Warrants).</footnote>
        <footnote id="F5">Pursuant to the Purchase Agreement dated as of February 18, 2010 by and among Overland Storage, Inc. and the investor named herein, the per unit price of a share of Series A Preferred Stock and Warrants exercisable for approximately eight shares of Common Stock is $15.00.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Jillian Mansolf</signatureName>
        <signatureDate>2010-03-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
