SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* McIlwain Matthew S (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Isilon Systems, Inc. [ ISLN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 04/26/2010
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) X Form filed by One Reporting Person Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	04/26/2010		J(1)		3,210	A	(2)	34,960(3)	D
Common Stock	04/26/2010		S		100,000	D	$13.8537(4)	8,614,176	I	See footnote(5)
Common Stock	04/26/2010		J(6)		1,490,439	D	(2)	7,123,737	I	See footnote(7)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Pro rata distribution of shares by Madrona Venture Fund I-B, LP and Madrona Managing Director Fund, LLC to their respective limited partners and members. The reporting person is a managing director and member of various entities affiliated with Madrona Venture Group, LLC.

2. Not applicable.

3. 4,000 shares were acquired through reporting person's 401k plan.

4. Represents a weighted-average price. These shares were sold in multiple transactions at prices ranging from $13.46 to $14.02, 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.

5. Represents 6,945,543 shares held by Madrona Venture Fund I-A, LP, 755,940 shares held by Madrona Venture Fund I-B, LP and 912,693 shares held by Madrona Managing Director Fund, LLC. The reporting person is a managing director and member of various entities affiliated with Madrona Venture Group, LLC. The reporting person 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.

6. Pro rata distribution of shares by Madrona Venture Fund I-A, LP, Madrona Venture Fund I-B, LP and Madrona Managing Director Fund, LLC to their respective limited partners and members. The reporting person is a managing director and member of various entities affiliated with Madrona Venture Group, LLC. The reporting person 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.

7. Represents 5,743,803 shares held by Madrona Venture Fund I-A, LP, 625,151 shares held by Madrona Venture Fund I-B, LP and 754,783 shares held by Madrona Managing Director Fund, LLC. The reporting person is a managing director and member of various entities affiliated with Madrona Venture Group, LLC. The reporting person 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.

	Keenan Conder, Attorney-in-Fact	04/28/2010
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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