<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-07-02</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000731502</issuerCik>
        <issuerName>MCDATA CORP</issuerName>
        <issuerTradingSymbol>MCDT</issuerTradingSymbol>
</issuer>
<reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001245081</rptOwnerCik>
            <rptOwnerName>GUSTAFSON MICHAEL B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>SVP Marketing</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeSecurity><securityTitle><value>McDATA Class B Common Stock</value>
</securityTitle>
<transactionDate><value>2003-07-02</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>S</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>2000</value>
<footnoteId id="F1"></footnoteId>
</transactionShares>
<transactionValue><value>14.39</value>
</transactionValue>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>42750</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeSecurity>
<nonDerivativeSecurity><securityTitle><value>McDATA Class B Common Stock</value>
</securityTitle>
<transactionDate><value>2003-07-02</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>S</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>1000</value>
<footnoteId id="F1"></footnoteId>
</transactionShares>
<transactionValue><value>14.36</value>
</transactionValue>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>42750</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeSecurity>
<footnotes><footnote id="F1">Sold pursuant to a 10b5-1 Plan</footnote>
</footnotes>
<ownerSignature><signatureName>Michael B. Gustafson</signatureName>
<signatureDate>2003-06-25</signatureDate>
</ownerSignature>
</ownershipDocument>

