X0202 3 2008-02-01 0 0001373671 Isilon Systems, Inc. ISLN 0001381752 McIlwain Matthew S C/O MADRONA VENTURE GROUP 1000 SECOND AVE., STE. 3700 SEATTLE WA 98104 true false false false Common Stock 4600 D Common Stock 8509117 I See footnote 4,000 shares were acquired through reporting person's 401k plan. Represents (a) 6,860,834 shares of common stock held by MadronaVenture Fund I-A, LP; (b) 746,721 shares of common stock held by Madrona Venture Fund I-B, LP; and (c) 901,562 shares of common stock held by Madrona Managing Director Fund LLC. Mr. McIlwain is a managing partner and member of various entities affiliated with Madrona Venture Group. Mr. McIlwain does not have sole voting or dispositive authority over these shares and disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. Cheryl Claeys, Attorney-in-Fact 2008-02-08