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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001104659-10-045074.txt : 20100818
<SEC-HEADER>0001104659-10-045074.hdr.sgml : 20100818
<ACCEPTANCE-DATETIME>20100818181612
ACCESSION NUMBER:		0001104659-10-045074
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100816
FILED AS OF DATE:		20100818
DATE AS OF CHANGE:		20100818

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ATLAS VENTURE FUND V LP
		CENTRAL INDEX KEY:			0001106910
		STATE OF INCORPORATION:			DE

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33196
		FILM NUMBER:		101026512

	BUSINESS ADDRESS:	
		STREET 1:		222 BERKELEY ST
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		6178599290

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Isilon Systems, Inc.
		CENTRAL INDEX KEY:			0001373671
		STANDARD INDUSTRIAL CLASSIFICATION:	COMPUTER STORAGE DEVICES [3572]
		IRS NUMBER:				912101027
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		3101 WESTERN AVENUE
		CITY:			SEATTLE
		STATE:			WA
		ZIP:			98121
		BUSINESS PHONE:		206-315-7500

	MAIL ADDRESS:	
		STREET 1:		3101 WESTERN AVENUE
		CITY:			SEATTLE
		STATE:			WA
		ZIP:			98121

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ATLAS VENTURE ASSOCIATES V LP
		CENTRAL INDEX KEY:			0001133805
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33196
		FILM NUMBER:		101026510

	BUSINESS ADDRESS:	
		STREET 1:		222 BERKELEY STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		6178599290

	MAIL ADDRESS:	
		STREET 1:		222 BERKELEY STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			ATLAS VENTURE ENTREPRENEURS FUND V LP
		CENTRAL INDEX KEY:			0001133807
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-33196
		FILM NUMBER:		101026511

	BUSINESS ADDRESS:	
		STREET 1:		222 BERKELEY STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		6178599290

	MAIL ADDRESS:	
		STREET 1:		222 BERKELEY STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
</SEC-HEADER>
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<TYPE>4
<SEQUENCE>1
<FILENAME>a4.xml
<DESCRIPTION>4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-08-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001373671</issuerCik>
        <issuerName>Isilon Systems, Inc.</issuerName>
        <issuerTradingSymbol>ISLN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001106910</rptOwnerCik>
            <rptOwnerName>ATLAS VENTURE FUND V LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>890 WINTER STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001133807</rptOwnerCik>
            <rptOwnerName>ATLAS VENTURE ENTREPRENEURS FUND V LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>890 WINTER STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001133805</rptOwnerCik>
            <rptOwnerName>ATLAS VENTURE ASSOCIATES V LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>890 WINTER STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>225000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.2743</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13350090</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>152000</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.8408</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13198090</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-08-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>68000</value>
                    <footnoteId id="F7"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.584</value>
                    <footnoteId id="F8"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13130090</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F9"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Sale of 222,039 shares of the Issuer's Common Stock by Atlas Venture Fund V, L.P. (&quot;Atlas V&quot;) and of 2,961 shares of the Issuer's Common Stock held by Atlas Venture Entrepreneurs' Fund V, L.P. (&quot;AVE V&quot;).  These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F2">Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $17.00 to $17.52, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.</footnote>
        <footnote id="F3">Represents aggregate shares beneficially owned after the reported transaction.  Includes 13,174,431 shares held directly by Atlas V and 175,659 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F4">Sale of 150,000 shares of the Issuer's Common Stock by Atlas V and of 2,000 shares of the Issuer's Common Stock held by AVE V.  These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F5">Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $17.51 to $18.03, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.</footnote>
        <footnote id="F6">Represents aggregate shares beneficially owned after the reported transaction.  Includes 13,024,431 shares held directly by Atlas V and 173,659 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F7">Sale of 67,105 shares of the Issuer's Common Stock by Atlas V and of 895 shares of the Issuer's Common Stock held by AVE V.  These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F8">Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $17.50 to $17.75, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.</footnote>
        <footnote id="F9">Represents aggregate shares beneficially owned after all of the reported transactions.  Includes 12,957,326 shares held directly by Atlas V and 172,764 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V.  Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V.  Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
    </footnotes>

    <remarks>This statement on Form 4 is filed by Atlas Venture Associates V, L.P., Atlas Venture Fund V, L.P., and Atlas Venture Entrepreneurs' Fund V, L.P.  The principal business address of each of the reporting persons is 890 Winter Street, Suite 320, Waltham, Massachusetts 02451.  The reporting persons disclaim beneficial ownership of the securities listed herein except to the extent of their pecuniary interest therein.</remarks>

    <ownerSignature>
        <signatureName>Atlas Venture Fund V, L.P., By: Atlas Venture Associates V, L.P., Its General Partner, By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President</signatureName>
        <signatureDate>2010-08-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Atlas Venture Entrepreneurs' Fund V, L.P., By: Atlas Venture Associates V, L.P., Its General Partner, By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President</signatureName>
        <signatureDate>2010-08-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Atlas Venture Associates V, L.P., By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President</signatureName>
        <signatureDate>2010-08-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
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