X0202 3 2006-12-14 0 0001373671 Isilon Systems, Inc. ISLN 0001103543 MADRONA VENTURE FUND I-A L P 1000 SECOND AVENUE SUITE 3700 SEATTLE WA 98104 0 0 1 0 0001103465 MADRONA VENTURE FUND I-B, LP 1000 SECOND AVENUE SUITE 3700 SEATTLE WA 98104 0 0 1 0 0001107551 MADRONA MANAGING DIRECTOR FUND, LLC 1000 SECOND AVENUE SUITE 3700 SEATTLE WA 98104 0 0 1 0 0001382421 Madrona Investment Partners, LLC 1000 SECOND AVENUE SUITE 3700 SEATTLE WA 98104 0 0 1 0 Series A Preferred Stock Common Stock 2990473 I See footnote Series B Preferred Stock Common Stock 2697184 I See footnote Series C Preferred Stock Common Stock 2352684 I See footnote Series D Preferred Stock Common Stock 1670154 I See footnote Series E Preferred Stock Common Stock 298643 I See footnote These shares of Preferred Stock will automatically convert into shares of Common Stock upon the closing of the Issuer's initial public offering on a 1-for-1 basis. Not applicable. Reflects a 1-for-2.4 reverse stock split effected immediately prior to the filing date. These shares of Preferred Stock will automatically convert into shares of Common Stock upon the closing of the Issuer's initial public offering on a 1-for-1 basis. Includes 2,411,195 shares held by Madrona Venture Fund I-A, LP ("Madrona Venture Fund A"), 262,430 shares held by Madrona Venture Fund I-B, LP ("Madrona Venture Fund B") and 316,848 shares held by Madrona Managing Director Fund LLC ("Madrona Managing Director Fund"). Matthew McIlwain (who is a director of the Issuer and files separate Section 16(a) reports) is a managing director of various entities affiliated with Madrona. Madrona Investment Partners, LLC is the general partner of Madrona Venture Fund A and Madrona Venture Fund B. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. Includes 2,174,726 shares held by Madrona Venture Fund A, 236,688 shares held by Madrona Venture Fund B and 285,770 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. Includes 1,896,958 shares held by Madrona Venture Fund A, 206,456 shares held by Madrona Venture Fund B and 249,270 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. Includes 1,346,637 shares held by Madrona Venture Fund A, 146,562 shares held by Madrona Venture Fund B and 176,955 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. Includes 240,795 shares held by Madrona Venture Fund A, 26,207 shares held by Madrona Venture Fund B and 31,641 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. /s/ Matthew S. McIlwain 2006-12-12 Matthew S. McIlwain 2006-12-12 Matthew S. McIlwain 2006-12-12 Matthew S. McIlwain 2006-12-12