X0303 4 2010-05-03 0 0001373671 Isilon Systems, Inc. ISLN 0001103543 MADRONA VENTURE FUND I-A L P 1000 SECOND AVE., SUITE 3700 SEATTLE WA 98104 0 0 1 0 0001103465 MADRONA VENTURE FUND I-B, LP 1000 SECOND AVE., SUITE 3700 SEATTLE WA 98104 0 0 1 0 0001107551 MADRONA MANAGING DIRECTOR FUND, LLC 1000 SECOND AVE. 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 Common Stock 2010-05-03 4 S 0 50000 13.57 D 7073737 D Common Stock 2010-05-04 4 S 0 50000 13.8808 D 7023737 D Represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $12.97 to $13.83, inclusive. For all transactions reported in this Form 4 utilizing a weighted-average price, the reporting person will provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. Represents 5,703,488 shares held by Madrona Venture Fund I-A, LP, 620,763 shares held by Madrona Venture Fund I-B, LP and 749,486 shares held by Madrona Managing Director Fund, LLC. Madrona Investment Partners, LLC is the general partner of Madrona Venture Fund I-A, LP and Madrona Venture Fund I-B, LP and disclaims beneficial ownership of the shares except to the extent of its pecuniary interest therein. Represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $13.44 to $14.29, inclusive. For all transactions reported in this Form 4 utilizing a weighted-average price, the reporting person will provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. Represents 5,663,173 shares held by Madrona Venture Fund I-A, LP, 616,375 shares held by Madrona Venture Fund I-B, LP and 744,189 shares held by Madrona Managing Director Fund, LLC. Madrona Investment Partners, LLC is the general partner of Madrona Venture Fund I-A, LP and Madrona Venture Fund I-B, LP and disclaims beneficial ownership of the shares except to the extent of its pecuniary interest therein. Troy Cichos 2010-05-05