Document:

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                                                                   EXHIBIT 10.12

September 29, 2004

Mr. John Briant

Dear John:

     It gives me great pleasure to offer you the position of Vice President of
Manufacturing and Operations for Isilon Systems, Inc. ("Isilon" or the
"Company"), We believe that you will add substantially to the team and
contribute greatly to the ultimate success of the Company by providing Isilon
with the same extraordinary leadership that you have demonstrated throughout
your career. The Board of Directors, the existing Isilon team and I look forward
to you joining the Company and helping us build Isilon into one of the most
important companies driving the next generation of storage solutions.

     We understand and appreciate the nature of the commitment you are making to
join Isilon, and we want you to do so with great confidence. You have the
qualities that distinguish successful executives: leadership, high integrity,
intelligence, action-oriented, and a desire to make a difference. We are
extremely enthusiastic about your acceptance of this offer.

     The Company is pleased to offer you employment on the following terms:

POSITION

     You will become Vice President of Manufacturing and Operations of the
Company, working out of the Company's headquarters office in Seattle,
Washington. You will report to the President and Chief Executive Officer. By
signing this letter agreement, you confirm to the Company that you have no
contractual commitments or other legal obligations that would prohibit you from
performing your duties for the Company.

START DATE

     Subject to fulfillment of any condition imposed by this letter agreement,
you will begin this new position with the Company at a mutually agreed upon
date. The Company would like you to begin your employment at Isilon no later
than November 15, 2004.

PROOF OF RIGHT TO WORK

     This offer of employment is contingent upon you presenting, in accordance
with applicable law, verification of your identity and your legal right to work
in the United States. In the event that you do not possess, or are unable to
obtain authorization to accept employment in the United States, our offer of
employment is withdrawn.

<PAGE>

COMPENSATION

     -    BASE SALARY. You will be paid a monthly salary of $14,583, which is
          equivalent to $175,000 on an annual basis. Your salary will be payable
          in twenty-six equal payments, one payment every two weeks, pursuant to
          the Company's regular payroll policy and will be subject to applicable
          withholding taxes.

     -    BONUS. You will be paid $12,500 bonus, subject to applicable
          withholding taxes, on your first pay period with the Company. As
          agreed, the purpose of this bonus is to cover the costs associated
          with home improvements prior to sale.

     -    TRAVEL BUDGET. The company will cover the cost of travel expenses, not
          to exceed mutually agreed upon budget amount, to and from Arizona and
          Washington for you and your family for the period from your Start Date
          until your family has relocated to Seattle.

     -    HOUSING BUDGET. The company will cover rental costs for an apartment
          in the Queen Anne area of Seattle, WA up to a maximum of $2,000 per
          month. The housing allowance will begin the first month of your
          employment with the Company and will be paid through the month in
          which your family relocates to Seattle, or May 2005, whichever date is
          sooner.

     -    RELOCATION BUDGET. The company will cover the cost of moving your
          household goods from Arizona to Seattle, WA, not to exceed a mutually
          agreed upon budget amount. All costs related to your move will be
          expensed and paid by the Company, or directly billed to the Company.

STOCK OPTIONS

     -    INITIAL OPTION GRANT. In connection with the commencement of your
          employment, the Company will recommend that the Board of Directors
          grant you an option to purchase 700,000 shares (approximately 0.7% of
          the fully-diluted shares post-series C financing) of the Company's
          Common Stock with an exercise price equal to the fair market value on
          the date of the grant. These option shares will vest at the rate of
          25% of the shares on the twelve (12) month anniversary of your Vesting
          Commencement Date (which will be the date your full-time employment
          with the Company commences) and the remaining shares will vest monthly
          thereafter at the rate of 1/48 of the total number of shares per
          month. Vesting will, of course, depend on your continued employment
          with the Company. The option will be an incentive stock option to the
          maximum extent allowed by the tax code and will be subject to the
          terms of the Company's 2001 Stock Option Plan and the Stock Option
          Agreement between you and the Company.

     -    EARLY EXERCISE PROVISION. In connection with the commencement of your
          employment, the Company will recommend that the Board of Directors
          offer you the option of exercising your "Initial Option Grant", as
          described above, within 45 days of your option grant being approved by
          the Company's Board of Directors. Should you choose this early
          exercise elective:

                                      -2-

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               -    You will be required to pay the full cost of exercising your
                    options, to the Company, within 45 days of your option grant
                    being approved by the Company's Board of Directors.

               -    Initially all of your exercised shares will be subject to
                    being repurchased by the company should your employment with
                    the company be terminated for any reason. On the twelve (12)
                    month anniversary of your Vesting Commencement Date (which
                    will be the date your full-time employment with the company
                    commences), 25% of your shares will be released from this
                    repurchase agreement and the remaining shares will be
                    released from this repurchase agreement at the rate of 1/48
                    of the total number of shares per month. Release of shares
                    from this repurchase agreement will, of course, depend on
                    your continued employment with the Company. Should the
                    Company exercise its option to repurchase your shares, the
                    Company will repurchase them at a price equivalent to your
                    original price per share.

               -    The early exercise agreement will impose restrictions on
                    unvested shares, including, but not limited to, limitations
                    on transfer, voting privileges, and escrow of unvested
                    shares.

     -    EQUITY BONUS. Upon the six month anniversary of your employment with
          the Company, and the successful achievement of mutually agreed upon
          MBOs associated with those milestones, the Company will recommend that
          the Board of Directors grant you an option to purchase 150,000 shares,
          (approximately 0.15% of the then current fully-diluted shares) of the
          Company's Common Stock, which shall be subject to the Plan. Such
          options will have an exercise price equal to the fair market value on
          the date of the approval of such grant by the Board and shall vest
          monthly over four years from your Start Date. These shares will also
          be eligible for the Company's Early Exercise Provision described
          above.

     -    SUBSEQUENT OPTION GRANTS. At the discretion of the Company' s Board of
          Directors, you may be eligible to receive additional grants of stock
          options or purchase rights from time to time in the future, on such
          terms and subject to such conditions as the Board of Directors shall
          determine as of the date of such grant.

BENEFITS

     -    INSURANCE BENEFITS. The Company will provide you with standard medical
          and dental insurance benefits according to Company policy. In
          addition, the Company will pay the COBRA premiums for your dependents
          for up to one year from your Start Date. This may be recognized as
          taxable income, in which case the Company will gross-up the additional
          amount to ensure there are no negative tax consequences associated
          with these payments.

     -    VACATION. You will be entitled to vacation according to Company
          policy.

                                      -3-

<PAGE>

PROPRIETARY INFORMATION AND INVENTIONS AGREEMENT

     Your acceptance of this offer and commencement of employment with the
Company is contingent upon the execution, and delivery to an officer of the
Company, of the Company's Proprietary Information and Invention Assignment
Agreement, a copy of which is enclosed for your review and execution (the
"Assignment Agreement"), prior to or on your Start Date.

AT-WILL EMPLOYMENT

     Your employment with the Company will be on an "at will" basis, meaning
that either you or the Company may terminate your employment at any time for any
reason or no reason, without further obligation or liability.

REFERENCE CHEEKS

     This offer of employment is contingent upon satisfactory reference checks,
to be conducted by Isilon.

ACCEPTANCE

     We are all delighted to be able to extend you this offer and look forward
to working with you. To indicate your acceptance of the Company's offer, please
sign and date this letter in the space provided below and return it to me, along
with a signed and dated copy of the Assignment Agreement, on or before Friday,
October 1, 2004 at 5:00 pm PST.

     This letter, together with the Assignment Agreement, set forth the terms of
your employment with the Company and supersedes any prior representations or
agreements, whether written or oral.

                                      -4-

<PAGE>

     This letter may not be modified or amended except by a written agreement,
signed by the Company and by you.

                                        Very truly yours,

                                        ISILON SYSTEMS, INC.

                                        By: /s/ Steve Goldman
                                            ------------------------------------
                                            Steve Goldman
                                            President and CEO

ACCEPTED AND AGREED:

JOHN BRIANT

/s/ John Briant
-------------------------------------
Signature

10/01/2004
Date

Enclosure A: Proprietary Information and Invention Assignment Agreement

                                      -5-<PAGE>

                                                                   EXHIBIT 10.13

March 29, 2004

Mr. Stuart Fuhlendorf

Dear Stu:

     It gives me great pleasure to offer you the position of Chief Financial
Officer and Vice President of Finance for Isilon Systems, Inc. ("Isilon" or the
"Company"). We believe that you will add substantially to the team and
contribute greatly to the ultimate success of the Company by providing Isilon
with the same extraordinary leadership that you have demonstrated throughout
your career. The Board of Directors, the existing Isilon team and I look forward
to you joining the Company and helping us build Isilon into one of the most
important companies driving the next generation of storage solutions.

     We understand and appreciate the nature of the commitment you are making to
join Isilon, and we want you to do so with great confidence. You have the
qualities that distinguish successful executives: leadership, high integrity,
intelligence, action-oriented, and a desire to make a difference. We are
extremely enthusiastic about your acceptance of this offer.

     The Company is pleased to offer you employment on the following terms:

POSITION

     You will become Chief Financial Officer and Vice President of Finance of
the Company, working out of the Company's headquarters office in Seattle,
Washington. You will report to the President and Chief Executive Officer. By
signing this letter agreement, you confirm to the Company that you have no
contractual commitments or other legal obligations that would prohibit you from
performing your duties for the Company.

START DATE

     Subject to fulfillment of any condition imposed by this letter agreement,
you will begin this new position with the Company at a mutually agreed upon
date. The Company would like you to begin your employment at Isilon no later
than April 26, 2004.

PROOF OF RIGHT TO WORK

     This offer of employment is contingent upon you presenting, in accordance
with applicable law, verification of your identity and your legal right to work
in the United States. In the event that you do not possess, or are unable to
obtain authorization to accept employment in the United States, our offer of
employment is withdrawn.

<PAGE>

COMPENSATION

     -    BASE SALARY. You will be paid a monthly salary of $12,500, which is
          equivalent to $150,000 on an annual basis. Your salary will be payable
          in twenty-six equal payments, one payment every two weeks, pursuant to
          the Company's regular payroll policy and will be subject to applicable
          withholding taxes.

     -    BONUS. Upon the successful achievement of mutually agreed upon
          Management by Objectives (MBOs), you will receive a quarterly bonus of
          $5,000. Your annual salary plus target bonuses will total annual OTE
          of $170,000. These bonuses will be paid quarterly following each
          quarter in which the mutually agreed upon MBOs are achieved.

STOCK OPTIONS

     -    INITIAL OPTION GRANT. In connection with the commencement of your
          employment, the Company will recommend that the Board of Directors
          grant you an option to purchase 700,000 shares (approximately 0.7% of
          the fully-diluted shares post-series C financing) of the Company's
          Common Stock with an exercise price equal to the fair market value on
          the date of the grant. These option shares will vest at the rate of
          25% of the shares on the twelve (12) month anniversary of your Vesting
          Commencement Date (which will be the date your full-time employment
          with the Company commences) and the remaining shares will vest monthly
          thereafter at the rate of 1/48 of the total number of shares per
          month. Vesting will, of course, depend on your continued employment
          with the Company. The option will be an incentive stock option to the
          maximum extent allowed by the tax code and will be subject to the
          terms of the Company's 2001 Stock Option Plan and the Stock Option
          Agreement between you and the Company.

     -    EARLY EXERCISE PROVISION. In connection with the commencement of your
          employment, the Company will recommend that the Board of Directors
          offer you the option of exercising your "Initial Option Grant", as
          described above, within 45 days of your option grant being approved by
          the Company's Board of Directors. Should you choose this early
          exercise elective:

               -    You will be required to pay the full cost of exercising your
                    options, to the Company, within 45 days of your option grant
                    being approved by the Company's Board of Directors.

               -    Initially all of your exercised shares will be subject to
                    being repurchased by the company should your employment with
                    the company be terminated for any reason. On the twelve (12)
                    month anniversary of your Vesting Commencement Date (which
                    will be the date your full-time employment with the company
                    commences), 25% of your shares will be released from this
                    repurchase agreement and the remaining shares will be
                    released from this repurchase agreement at the rate of 1/48
                    of the total number of shares per month. Release of shares
                    from this repurchase agreement will, of course, depend on
                    your continued employment with the Company. Should the
                    Company exercise its option to repurchase your shares,

                                       -2-

<PAGE>

                    the Company will repurchase them at a price equivalent to
                    your original price per share.

               -    The early exercise agreement will impose restrictions on
                    unvested shares, including, but not limited to, limitations
                    on transfer, voting privileges, and escrow of unvested
                    shares.

     -    EQUITY BONUS. Upon the six month anniversary of your employment with
          the Company, and the successful achievement of mutually agreed upon
          MBOs associated with those milestones, the Company will recommend that
          the Board of Directors grant you an option to purchase 150,000 shares,
          (approximately 0.15% of the then current fully-diluted shares) of the
          Company's Common Stock, which shall be subject to the Plan. Such
          options will have an exercise price equal to the fair market value on
          the date of the approval of such grant by the Board and shall vest
          monthly over four years from your Start Date. These shares will also
          be eligible for the Company's Early Exercise Provision described
          above.

     -    SUBSEQUENT OPTION GRANTS. At the discretion of the Company's Board of
          Directors, you may be eligible to receive additional grants of stock
          options or purchase rights from time to time in the future, on such
          terms and subject to such conditions as the Board of Directors shall
          determine as of the date of such grant.

BENEFITS

     -    INSURANCE BENEFITS. The Company will provide you with standard medical
          and dental insurance benefits according to Company policy.

     -    VACATION. You will be entitled to vacation according to Company
          policy.

PROPRIETARY INFORMATION AND INVENTIONS AGREEMENT

     Your acceptance of this offer and commencement of employment with the
Company is contingent upon the execution, and delivery to an officer of the
Company, of the Company's Proprietary Information and Invention Assignment
Agreement, a copy of which is enclosed for your review and execution (the
"Assignment Agreement"), prior to or on your Start Date.

AT-WILL EMPLOYMENT

     Your employment with the Company will be on an "at will" basis, meaning
that either you or the Company may terminate your employment at any time for any
reason or no reason, without further obligation or liability.

REFERENCE CHECKS

     This offer of employment is contingent upon satisfactory reference checks,
to be conducted by Isilon.

                                       -3-

<PAGE>

ACCEPTANCE

     We are all delighted to be able to extend you this offer and look forward
to working with you. To indicate your acceptance of the Company's offer, please
sign and date this letter in the space provided below and return it to me, along
with a signed and dated copy of the Assignment Agreement, on or before
Wednesday, March 31, 2004 at 12:00 pm PST.

     This letter, together with the Assignment Agreement, set forth the terms of
your employment with the Company and supersedes any prior representations or
agreements, whether written or oral. This letter may not be modified or amended
except by a written agreement, signed by the Company and by you.

                            [SIGNATURE PAGE FOLLOWS]

                                       -4-

<PAGE>

                                        Very truly yours,

                                        ISILON SYSTEMS, INC.

                                        By: /s/ Steve Goldman
                                            ------------------------------------
                                            Steve Goldman
                                            President and CEO

ACCEPTED AND AGREED:

STUART FUHLENDORF

/s/ Stuart Fuhlendorf
-------------------------------------
Signature

3-30-04
Date

Enclosure A: Proprietary Information and Invention Assignment Agreement
Enclosure B: Isilon Systems' Travel and Entertainment Policy

                                       -5-

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