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| 1. | I                  have reviewed this annual                  report on Form 10-K of Isilon Systems,                  Inc.; |
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| 2. | Based                    on my knowledge, this                    report does not contain any untrue statement of a material fact                    or omit to                    state a material fact necessary to make the statements made,                    in light of                    the circumstances under which such statements were made, not                    misleading                    with respect to the period covered by this                    report; |
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| 3. | Based                    on my knowledge, the                    financial statements, and other financial information included                    in this                    report, fairly present in all material respects the financial                    condition,                    results of operations and cash flows of the registrant as of,                    and for, the                    periods presented in this                    report; |
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| 4. | The                    registrant’s other certifying officer(s) and I are responsible for                    establishing and maintaining disclosure controls and procedures                    (as                    defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal                    controls over financial reporting (as defined in Exchange Act                    Rules                    13a-15(f) and 15d-15(f))  for the registrant and                    have: |
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|   | a. | Designed                  such disclosure controls                  and procedures, or caused such disclosure controls and procedures                  to be                  designed under our supervision, to ensure that material information                  relating to the registrant, including its consolidated subsidiaries,                  is                  made known to us by others within those entities, particularly                  during the                  period in which this report is being                  prepared; |
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|   | b. | Designed                  such internal control                  over financial reporting, or caused such internal control over                  financial                  reporting to be designed under our supervision, to provide reasonable                  assurance regarding the reliability of financial reporting and                  the                  preparation of financial statements for external purposes in accordance                  with generally accepted accounting                  principles; |
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|   | c. | Evaluated                  the effectiveness of                  the registrant’s disclosure controls and procedures and presented in this                  report our conclusions about the effectiveness of the disclosure                  controls                  and procedures, as of the end of the period covered by this report                  based                  on such evaluation; and |
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|   | d. | Disclosed                  in this report any                  change in the registrant’s internal control over financial reporting that                  occurred during the registrant’s most recent fiscal quarter (the                  registrant’s fourth fiscal quarter in the case of an annual report) that                  has materially affected, or is reasonably likely to materially                  affect, the                  registrant’s internal control over financial reporting;                  and |
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| 5. | The                  registrant’s other certifying                  officer(s) and I have disclosed, based on our most recent evaluation                  of                  internal control over financial reporting, to the registrant’s auditors                  and the audit committee of the registrant’s board of directors (or persons                  performing the equivalent                  functions): |
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|   | a. | All                  significant deficiencies and                  material weaknesses in the design or operation of internal control                  over                  financial reporting which are reasonably likely to adversely affect                  the                  registrant’s ability to record, process, summarize and report financial                  information; and |
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|   | b. | Any                  fraud, whether or not                  material, that involves management or other employees who have                  a                  significant role in the registrant’s internal control over financial                  reporting. |
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|                               |                                                        |   |
|------------------------------------|-------------------------------------------------------------|--------|
| Date:                April 2, 2008 | /s/                WILLIAM RICHTER                          |   |
|                               | William                Richter                              |   |
|                               | Interim                Chief Financial Officer and          |   |
|                               | (Principal                Accounting and Financial Officer) |   |

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