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                                                                    EXHIBIT 10.3

                             UNCONDITIONAL GUARANTY

                                      from

                           IRON MOUNTAIN INCORPORATED
                                  as Guarantor

                                       to

                      IRON MOUNTAIN STATUTORY TRUST - 1999
                                    as Owner

                            Dated as of July 1, 1999
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      THIS UNCONDITIONAL GUARANTY, dated as of July 1, 1999 (herein, together
with all amendments and supplements hereto, called this Guaranty), is from Iron
Mountain Incorporated, a Delaware corporation (herein, together with its
successors and assigns, called Guarantor), having an address at 745 Atlantic
Avenue, Boston, Massachusetts 02111, Attention: Treasurer, to Iron Mountain
Statutory Trust - 1999, a Connecticut statutory trust (herein together with its
successors and assigns, called Owner), having an address at c/o First Union
National Bank, 10 State House Square, Hartford, Connecticut 06103, Attention:
Corporate Trust Administration. Terms not otherwise defined herein shall have
the meanings set forth in Appendix I to the Lease (as hereinafter defined).

                              Preliminary Statement

      Owner has entered into a Lease Agreement dated as of the date hereof with
Iron Mountain Records Management, Inc. (herein called Lessee) (said Lease
Agreement, as supplemented or amended from time to time, including without
limitation by a Lease Supplement, herein called the Lease) relating to the
Properties. Pursuant to the terms of the Lease, Lessee shall lease the
Properties from Owner for a term of years, as more particularly set forth in the
Lease. Owner has also entered into an Agency Agreement dated as of the date
hereof (herein called the Agency Agreement) with Lessee, as agent. Pursuant to
the terms of the Agency Agreement, Lessee shall, as agent for Owner, acquire
Properties and otherwise perform certain obligations relating thereto, all as
more particularly set forth in the Agency Agreement. Guarantor is the owner of
all of the issued and outstanding stock of Lessee. In order to induce Owner to
enter into the Lease and the Agency Agreement and to enter into the leasing and
agency arrangements with Lessee, as more particularly described therein,
Guarantor has entered into this Guaranty with respect to the obligations of
Lessee under the Lease and the Agency Agreement.

      NOW, THEREFORE, in consideration of the premises, and for other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, Guarantor agrees as follows:

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      1. Guarantor unconditionally and irrevocably guaranties to (a) Owner, and
(b) to the extent of Lessee's obligations to the Indemnified Parties, the
Indemnified Parties, the prompt payment and performance of all obligations of
Lessee under the Lease and the Agency Agreement (all of the foregoing
collectively, the Guaranteed Obligations). This Guaranty is an irrevocable,
absolute, present, primary, continuing, unlimited and unconditional promise with
respect to the full and punctual payment and performance by Lessee of each of
the Guaranteed Obligations, and is not a promise of collectibility only, and is
in no way conditional upon the requirement that Owner first attempt to collect
payment or demand performance from Lessee or that Owner resort to any security
or other means of obtaining such payment or performance or upon any other
contingency. If for any reason (i) any such sums shall not be paid promptly by
Lessee when due, or (ii) any such covenant, agreement, term or condition is not
performed or observed by Lessee in accordance with the Lease or the Agency
Agreement, Guarantor, shall, without notice or demand of any nature, pay the
same by wire transfer of immediately available federal funds to the Person or
Persons entitled thereto pursuant to the provisions of said instruments and
shall perform and observe or cause to be promptly performed and observed every
such covenant, agreement, term and condition, in each case regardless of (i) any
defenses or rights of set-off or counterclaims which Guarantor or Lessee may
have or assert, (ii) whether Owner shall have taken any steps to enforce any
rights against Lessee or any other remedy thereunder as a result of the default
of Lessee thereunder and (iii) any other event, condition, contingency or
circumstance whatsoever. Guarantor also agrees to pay to such Persons such
further amounts as shall be sufficient to cover the costs and expenses of
collecting such sums or any part thereof, or of otherwise enforcing or
protecting the rights of such Persons under the Lease, the Agency Agreement and
this Guaranty, including reasonable fees and expenses of its attorneys and to
Owner and its attorneys for all services rendered in that connection and in any
related proceeding.

      2. The obligations, covenants, agreements and duties of Guarantor under
this Guaranty shall be absolute and unconditional, shall not be subject to any
counterclaim, setoff,

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deduction, diminution, abatement, recoupment, suspension, deferment, reduction
or defense based upon any claim that Guarantor or any other Person may have
against Lessee, Owner or any other Person, and, until the payment or performance
in full of the Guaranteed Obligations, shall remain in full force and effect
without regard to, and shall not be released, discharged or in any way affected
by, any circumstance or condition whatsoever (whether or not Owner, Guarantor or
Lessee shall have any knowledge or notice thereof), including, without
limitation, the happening from time to time of any of the following, although
without notice to, or the consent of, Guarantor:

      (a)   the waiver by Owner of the performance or observance by Lessee,
            Guarantor or any other party of any of the agreements, covenants,
            terms or conditions contained in the Lease, the Agency Agreement,
            this Guaranty or any other instrument or Operative Document;

      (b)   the extension, in whole or in part, of the time for payment by
            Lessee or Guarantor of any sums owing or payable under the Lease,
            the Agency Agreement or this Guaranty, as applicable, or of any
            other sums of obligations under or arising out of or on account of
            the Lease, the Agency Agreement, this Guaranty or the renewal or
            extension of either thereof;

      (c)   any assignment or subsequent reassignment of the Lease, the Agency
            Agreement or this Guaranty, in whole or in part, or the leasing or
            subletting of any Property or any part thereof;

      (d)   the modification or amendment (whether material or otherwise) of any
            of the obligations of Lessee or Guarantor under the Lease, the
            Agency Agreement, this Guaranty or any other Operative Document, as
            applicable;

      (e)   the taking or the omission of any of the acts referred to in the
            Lease, the Agency Agreement, this Guaranty or any other Operative
            Document (including, without limitation, the giving of any consent
            referred to herein or therein, but excepting therefrom those acts
            and omissions permitted in compliance with and pursuant to the terms
            of the Lease or the Agency Agreement, as the case may be, and any
            assignment or reassignment thereof or this Guaranty and any
            assignment or reassignment hereof, as appropriate);

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      (f)   any failure, omission or delay on the part of Owner to enforce,
            assert or exercise any right, power or remedy conferred on or
            available to Owner in or by the Lease, the Agency Agreement, this
            Guaranty or any other instrument, or any action on the part of Owner
            granting indulgence or extension in any form whatsoever;

      (g)   the voluntary or involuntary liquidation, dissolution, sale of all
            or substantially all of the assets, marshaling of assets and
            liabilities, receivership, conservatorship, insolvency, bankruptcy,
            assignment for the benefit of creditors, reorganization,
            arrangement, composition or readjustment of, or other similar
            proceeding affecting, Owner, Lessee or Guarantor or any of their
            respective assets;

      (h)   the release of Lessee or Guarantor from the performance or
            observance of any of the agreements, covenants, terms or conditions
            contained in the Lease, the Agency Agreement, this Guaranty or any
            other Operative Document, as applicable, by operation of law or
            otherwise, except for those releases given or made in compliance
            with and pursuant to the terms of the Lease, the Agency Agreement,
            as applicable, and any assignment or reassignment thereof, or this
            Guaranty and any assignment or reassignment hereof, as applicable,
            or any invalidity or unenforceability of the Lease, the Agency
            Agreement or this Guaranty or any other Operative Document;

      (i)   any defect in the title, or any damage to or loss or destruction of,
            or any interruption or cessation in the use of any Property or any
            portion thereof by Lessee for any reason whatsoever (including,
            without limitation, any governmental prohibition or restriction,
            condemnation, requisition, or any other act on the part of any
            governmental authority, or any act of Force Majeure) regardless of
            the duration thereof (even though such duration would otherwise
            constitute a frustration of the Lease or the Agency Agreement, as
            the case may be), whether or not resulting from accident and whether
            or not without fault on the part of Lessee or any other Person;

      (j)   the inability of Owner or Lessee to enforce any provision of the
            Lease or the Agency Agreement for any reason;

      (k)   any merger or consolidation of Lessee or Guarantor into or with any
            other corporation or any sale, lease or transfer of any of the
            assets of Lessee or Guarantor to any other Person;

      (l)   any change in the corporate relationship between Guarantor and
            Lessee;

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      (m)   the acceptance and release by Owner of any other security or
            guarantor for any obligation hereunder;

      (n)   any value, estimation, termination, rejection, discharge or
            disaffirmance by any Person (including trustees, trustees in
            bankruptcy, liquidators or representatives) of the Guaranteed
            Obligations in connection with any insolvency, bankruptcy,
            reorganization or liquidation of Lessee or any proceeding relating
            thereto;

      (o)   any determination or claim that Owner's claims against Lessee are or
            may be limited by Section 502(b) (6) of the Bankruptcy Code, as
            amended, or to any similar or successor provision of law upon any
            rejection of the Lease or the Agency Agreement in a bankruptcy
            proceeding filed by or against Lessee;

      (p)   any failure or recharacterization of title with respect to Owner's,
            Lessee's or any other Person's interest in any Property; or

      (q)   any other occurrence or circumstance whatsoever, whether similar or
            dissimilar to the foregoing and any other circumstance that might
            otherwise constitute a legal or equitable defense or discharge of
            the liabilities of a guarantor or surety or that might otherwise
            limit recourse against Guarantor.

      The obligations of Guarantor set forth herein constitute the full recourse
obligations of Guarantor enforceable against Guarantor to the full extent of all
its assets and properties. In no event shall the obligations of Guarantor
hereunder be subordinated in any manner to any other full recourse obligations
of Guarantor.

      3. Guarantor unconditionally waives (i) notice of any of the matters
referred to in Section 2, (ii) all notices that may be required by statute, rule
of law or otherwise, now or hereafter in effect, to preserve intact any rights
against Guarantor, including, without limitation, any demand, presentment and
protest, proof of notice of non-payment under the Lease or the Agency Agreement
and notice of Default or Event of Default under the Lease or the Agency
Agreement or this Guaranty, or any failure on the part of Lessee to perform and
comply with any covenant, agreement, term or condition of the Lease or the
Agency Agreement, (iii) any right to the enforcement, assertion or exercise
against Lessee of any right, power, privilege or remedy conferred in the Lease
or the Agency Agreement or otherwise, (iv) any requirement of diligence

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on the part of Owner or any other Person, (v) any requirement that Owner take
any steps to enforce any rights against Lessee under the Lease or the Agency
Agreement or any other remedy thereunder or any other requirement to exhaust any
remedies or to mitigate the damages resulting from any Default or Event of
Default under the Lease or the Agency Agreement or this Guaranty, (vi) any
notice of any sale, transfer or other disposition of any right, title to or
interest in the Lease or the Agency Agreement or any Property covered thereby by
Owner, (vii) all rights of Guarantor under the laws of the states in which the
Properties are located, as the same may be amended, and (viii) any other
circumstance whatsoever that might otherwise constitute a legal or equitable
discharge, release or defense of a guarantor or surety, or that might otherwise
limit recourse against Guarantor hereunder.

      4. Notwithstanding any payment or payments made or obligation performed by
Guarantor by reason of this Guaranty, Guarantor hereby waives (i) any claim,
right or remedy that Guarantor may now or hereafter acquire against Lessee that
arises hereunder and/or by reason of any one or more payments or acts of
performance by Guarantor hereunder, including without limitation, any claim,
remedy or right of subrogation, reimbursement, exoneration, contribution,
indemnification or participation in any claim, right or remedy of the Owner
against Lessee or any security that Owner now has or hereafter acquires, whether
or not such claim, right or remedy arises in equity, under contract, by statute,
under common law or otherwise, (ii) any right to enforce any remedy which Lessee
or any other guarantor of Lessee's obligations now has or may hereafter have
against Owner or its assigns, and (iii) any right to enforce or exercise the
benefit of and any right to participate in, any security now or hereafter held
by Owner, in each case until all of the obligations guarantied hereby are
performed in full. If any amount shall nevertheless be paid to Guarantor by any
such Person in violation of this Guaranty, such amount shall be held by
Guarantor in trust for the benefit of Owner and shall forthwith be paid to
Owner. Guarantor further waives any defense to the recovery by Owner from
Guarantor of any deficiency or otherwise to the enforcement of this Guaranty
after a judicial or nonjudicial sale or other disposition of any security for or
any of the obligations of Lessee under the Lease or the

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Agency Agreement, even though such a sale may prevent Guarantor from exercising
rights of subrogation, if any, contribution or reimbursement against Lessee or
any other party. No payment hereunder by Guarantor shall give rise to any claim
by Guarantor against Owner, except for payments made in error by Guarantor to
the extent such payments are in excess of amounts due hereunder. Unless and
until all obligations of Lessee under and pursuant to the Lease and the Agency
Agreement, and of Guarantor hereunder, shall have been discharged by payment or
performance in full, Guarantor shall not assign or otherwise transfer any such
claim against Lessee to any other Person.

      5. The following events shall constitute Events of Default under this
Guaranty: (i) Guarantor shall fail to make any payment due hereunder upon
demand, or (ii) (a) there shall occur a breach of any of the covenants contained
in paragraph 10 hereof (other than those covenants incorporated by reference
from the Credit Agreement pursuant to paragraph 10(a)(vi) hereof, except to the
extent that a violation of any such covenant gives rise to an event of default
under the Credit Agreement); or (b) Guarantor shall fail to perform or observe
any other provision hereof and such failure shall continue for 25 days after
written notice thereof to Guarantor from Owner, or (iii) if any representation
or warranty made by Guarantor herein or in any document, certificate or notice
furnished by Guarantor to Owner in connection herewith or pursuant hereto shall
prove to be false or misleading as of the time when made in any material respect
as of the time made, or (iv) (a) if Guarantor shall commence a voluntary case
under any Bankruptcy Law or file a petition in bankruptcy or for reorganization
or for an arrangement pursuant to any Bankruptcy Law; (b) if Guarantor shall
file for an order of relief or be adjudicated a debtor or a bankrupt under any
Bankruptcy Law or become insolvent; (c) if Guarantor shall generally not pay its
debts as such debts become due or shall make an assignment for the benefit of
creditors or shall admit in writing its inability to pay its debts generally as
they become due; or (d) if an involuntary case against Guarantor as debtor is
commenced by a petition for reorganization or liquidation under any Bankruptcy
Law, or if a petition or answer proposing the adjudication of Guarantor as a
bankrupt or its reorganization

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pursuant to any Bankruptcy Law shall be filed in any court and Guarantor shall
consent to or acquiesce in the filing thereof or such case, petition or answer
shall not be dismissed, discharged or denied within 60 days after filing
thereof; or (v) if a custodian for purposes of any Bankruptcy Law of
substantially all Guarantor's assets is appointed or otherwise takes possession
thereof and such appointment remains in effect for more than 60 days; or (vi) if
a receiver, U.S. Trustee, trustee or liquidator of Guarantor or all or
substantially all of the assets of Guarantor shall be appointed in any
proceeding brought by Guarantor, or if any such receiver, U.S. Trustee, trustee
or liquidator shall be appointed in any proceeding brought against Guarantor and
shall not be discharged within 60 days after such appointment, or if Guarantor
shall consent to or acquiesce in such appointment; or (vii) if there is an Event
of Default under the Lease or the Agency Agreement; then, in each such case, so
long as the same shall be continuing, Owner may, at its option, declare this
Guaranty in default, and at any time thereafter, so long as Guarantor shall not
have remedied all outstanding Events of Default hereunder, Owner shall be
entitled to exercise any remedy available to it at law or in equity. No express
or implied waiver by Owner of an Event of Default hereunder shall in any way be,
or be construed to be a waiver of any further or subsequent Event of Default.
Guarantor hereby waives any right now or hereinafter conferred upon it by
statute or otherwise which may limit or modify any of Owner's rights and
remedies contained herein. Guarantor agrees to give written notice to Owner (a)
of any Event of Default hereunder promptly after the occurrence thereof and (b)
of any Event of Default hereunder or under the Lease or the Agency Agreement,
immediately after the President or Chief Financial Officer of Guarantor obtains
Actual Knowledge of the occurrence thereof.

      6. (a) In the event of a Default or Event of Default under the Agency
Agreement, Guarantor may, and in the event of the rejection or disaffirmation of
the Agency Agreement by Lessee as debtor in possession or Lessee's trustee in
bankruptcy pursuant to any Bankruptcy Law, Guarantor shall and does hereby
(without the necessity of any further agreement or act), assume all obligations
and liabilities of Lessee under the Agency Agreement to the same extent as if it
had been originally named instead of such Lessee as a party to such documents
and there

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had been no such rejection or disaffirmance; and Guarantor shall confirm such
assumption in writing at the request of Owner upon or after such rejection or
disaffirmance. Guarantor, upon such assumption, will have all rights of Lessee
under the Agency Agreement. From and after the date of such assumption, as
provided in this Section 6(a), all provisions of this Guaranty shall continue in
full force and effect as separate and independent undertakings of Guarantor,
binding upon and enforceable against Guarantor without regard to the validity or
enforceability of such assumption, and all provisions of this Guaranty
applicable to the Agency Agreement and to Owner and Lessee in respect of the
Agency Agreement shall also apply to such assumption and to Owner and Guarantor
in respect of such assumption to the same extent and in the same manner as such
provisions are applicable to the Agency Agreement and to Owner and Lessee in
respect of the Agency Agreement.

            (b) In the event of a Default or Event of Default under the Lease,
Guarantor may, and in the event of the rejection or disaffirmation of the Lease
by Lessee as debtor in possession or Lessee's trustee in bankruptcy pursuant to
any Bankruptcy Law, Guarantor shall and does hereby (without the necessity of
any further agreement or act), assume all obligations and liabilities of Lessee
under the Lease to the same extent as if it had been originally named instead of
such Lessee as a party to such documents and there had been no such rejection or
disaffirmance; and Guarantor shall confirm such assumption in writing at the
request of Owner upon or after such rejection or disaffirmance. Guarantor, upon
such assumption, will have all rights of Lessee under the Lease. From and after
the date of such assumption, as provided in this Section 6(b), all provisions of
this Guaranty shall continue in full force and effect as separate and
independent undertakings of Guarantor, binding upon and enforceable against
Guarantor without regard to the validity or enforceability of such assumption,
and all provisions of this Guaranty applicable to the Lease and to Owner and
Lessee in respect of the Lease shall also apply to such assumption and to Owner
and Guarantor in respect of such assumption to the same extent and in the same
manner as such provisions are applicable to the Lease and to Owner and Lessee in
respect of the Lease.

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      7. It is agreed that the liabilities and obligations of Guarantor
hereunder are primary and those of a principal, and are enforceable either
before, simultaneously with or after proceeding against Lessee or against any
property or security available to Owner.

      8. This Guaranty may not be modified or amended except by a written
agreement duly executed by Guarantor with the consent in writing of Owner, the
Agent Bank and the Lenders. Neither this Guaranty, nor any of the obligations of
Guarantor hereunder may be assigned to any Person or entity by Guarantor.

      9. Guarantor shall furnish the following financial statements to Owner:

            (a)   as soon as practicable, copies of all such financial
                  statements, proxy statements, notices, other communications
                  and reports as Guarantor shall send on a regular basis to its
                  shareholders and other information, if any, generally made
                  available to banks and other lenders (exclusive of proprietary
                  information);

            (b)   for any period that Guarantor is a public company, copies of
                  all reports on Form 10-K and Form 10-Q (and any successor
                  form) in each case together with a list describing all reports
                  filed with the Securities and Exchange Commission during the
                  reporting period, and any such listed reports shall be
                  delivered to Agent Bank and any Lender upon such Lender's
                  request which Guarantor is or may be required to file with the
                  Securities and Exchange Commission or any governmental body or
                  agency succeeding to the functions of the Securities and
                  Exchange Commission; and

            (c)   for any period that Guarantor is not a public company required
                  to file such reports with the Securities and Exchange
                  Commission, then within 105 days after the end of each fiscal
                  year, and within 60 days after the end of any other fiscal
                  quarter, financial statements containing substantially the
                  same information as the information that would be included in
                  such reports on Form 10-K or Form 10-Q, as the case may be,
                  and in any event, all in reasonable detail and satisfactory in
                  scope to Owner and Owner's mortgagee, all prepared in
                  accordance with GAAP and, with respect to the annual
                  statements, audited, by independent certified public
                  accountants of recognized national standing selected by
                  Guarantor.

Concurrently with the delivery of quarterly financial statements pursuant
hereto, Guarantor shall cause to be delivered to Owner an Officer's Certificate
(i) stating that to the best of the

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knowledge of the Applicable Officer executing such Officer's Certificate based
on reasonable inquiry, there exists no Default or Event of Default under the
Lease, the Agency Agreement or this Guaranty or if any such Default or Event of
Default exists, specifying the nature thereof, the period of existence thereof
and what action Guarantor proposes to take with respect thereto and (ii) setting
forth such information as shall be necessary for Owner and the Agent Bank to
confirm compliance by Guarantor with the covenants contained in Paragraph 10
hereof.

      10. (a) Guarantor hereby covenants and agrees as follows:

                  (i) Leverage Ratio. (A) The Guarantor will not, as at the end
of any fiscal quarter, permit the ratio, calculated as at the end of such fiscal
quarter for the period of four fiscal quarters then ended, of (i) the excess of
(x) the aggregate outstanding principal amount of Funded Indebtedness (on a
consolidated basis) of the Guarantor and its Subsidiaries at such date over (y)
the aggregate amount of cash and Liquid Investments of the Guarantor and its
Subsidiaries at such date to (ii) EBITDA for such period (the Leverage Ratio) to
exceed the ratio of 5.75 to 1.

      (B) The Guarantor will not, as at the end of any fiscal quarter, permit
the ratio, calculated as at the end of such fiscal quarter for the period of
four fiscal quarters then ended, of (i) the excess of (x) the aggregate
outstanding principal amount of Indebtedness (on a consolidated basis) of the
Pond Joint Venture and each Excluded Subsidiary at such date over (y) the
aggregate amount of cash and Liquid Investments of the Pond Joint Venture and
each Excluded Subsidiary at such date to (ii) EBITDA for such period (the
Foreign Leverage Ratio) to exceed 3.50 to 1. Solely for purposes of this
paragraph (B), in determining the Foreign Leverage Ratio, EBITDA shall be
determined by including only the Pond Joint Venture and each Excluded
Subsidiary.

                  (ii) Interest Coverage Ratio. Guarantor will not, as at the
end of any fiscal quarter, permit the ratio, calculated as at the end of such
fiscal quarter for the period of four fiscal quarters then ended, of (i) EBITDA
for such period to (ii) Interest Expense for such period to be less than the
ratio of 1.85 to 1.

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            For purposes of calculating any ratio set forth in this clause (ii),
if Guarantor elects pursuant to the penultimate sentence of the definition of
EBITDA set forth in paragraph (c) below to include in EBITDA for the period to
which such ratio relates the pro forma amounts referred to in such sentence,
there shall be included in Interest Expense for such period, on a pro forma
basis, interest accruing during such period on Indebtedness (and the interest
portion of payments under Capitalized Lease Obligations) assumed or incurred by
Guarantor and its Subsidiaries (on a consolidated basis) in connection with any
Permitted Acquisition having Acquisition Consideration of more than $500,000
during such period.

                  (iii) Fixed Charges Coverage Ratio. Guarantor will not, as at
the end of any fiscal quarter, permit the ratio, calculated as at the end of
such fiscal quarter for the period of four fiscal quarters then ended, of (i)
Adjusted EBITDA for such period to (ii) Fixed Charges for such period to be less
than the ratio of 1.4 to 1.

            For purposes of calculating any ratio set forth in this clause
(iii), if Guarantor elects pursuant to the penultimate sentence of the
definition of EBITDA to include in EBITDA for the period to which such ratio
relates the pro forma amounts referred to in such sentence, there shall be
included in Fixed Charges for such period, on a pro forma basis, principal
payable and interest accruing during such period on Indebtedness (and the
interest portion of payments under Capitalized Lease Obligations) assumed or
incurred by Guarantor and its Subsidiaries (on a consolidated basis) in
connection with any Permitted Acquisition having Acquisition Consideration of
more than $500,000 during such period.

                  (iv) Subordinated Indebtedness. Guarantor will maintain at all
times an aggregate principal amount of not less than $275,000,000 of
Subordinated Indebtedness. As used herein, "Subordinated Indebtedness" shall
mean Indebtedness that by its terms is equivalent or similar to Guarantor's
existing 10-1/8% Senior Subordinated Notes due 2006, the 8-3/4% Senior
Subordinated Notes due 2009, and the 8-1/4% Senior Subordinated Notes due 2011
which by its terms is subordinated to such Indebtedness.

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                  (v) Liens. Guarantor will not, and will not permit any of its
Subsidiaries to, create or suffer to exist any Lien upon any property or assets,
now owned or hereafter acquired, securing any Indebtedness or other obligation,
except: (i) Liens in favor of the agent bank and lenders under the Credit
Agreement on the capital stock and related proceeds of all Subsidiaries of the
Guarantor from time to time; (ii) the Liens existing on September 26, 1997 and
set forth on Schedule III to the Credit Agreement and Liens arising out of the
refinancing, extension, renewal or refunding of any Indebtedness secured by any
Lien set forth on such schedule, provided that the principal amount of such
Indebtedness is not increased and is not secured by any additional assets;
(iii)(A) Liens not otherwise prohibited by the Operative Documents contemplated
by or securing Indebtedness described in clauses (ii), (iv), (v) and (vii) of
the definition of Permitted Indebtedness set forth in the Credit Agreement; or
(B) Liens securing Acquired Debt, provided that such Liens cover only those
assets that were covered by such Liens prior to the relevant acquisition; (iv)
attachment, judgment or other similar Liens arising in connection with
litigation or other legal proceedings, provided that either (A) the claims in
respect of such Liens are fully covered by insurance or (B) the execution or
other enforcement of such Liens is effectively stayed and the claims secured
thereby are in an amount not to exceed $1,000,000 in the aggregate and are being
contested in good faith by appropriate proceedings diligently prosecuted; (v)
Liens on properties or assets of an Excluded Subsidiary securing Indebtedness of
such Excluded Subsidiary permitted under the Credit Agreement; (vi) other Liens
arising in the ordinary course of the business of the Guarantor or such
Subsidiary which are not incurred in connection with the borrowing of money or
the obtaining of advances or credit and which do not materially detract from the
value of its property or assets or materially impair the use thereof in the
operation of its business; (vii) Liens securing Indebtedness created or incurred
by the Pond Joint Venture or any Excluded Subsidiary, provided that such Liens
extend only to the assets of the Pond Joint Venture or any Excluded Subsidiary
incurring such Indebtedness as a primary obligor (and not as a guarantor) or
Capital Stock of the Pond Joint Venture or such Excluded Subsidiary; and (viii)
Liens arising under or created pursuant to the

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                                       14


Lease or the Lease Agreement between Lessee and Iron Mountain Statutory Trust -
1998 dated as of October 1, 1998, as amended or supplemented from time to time.

                  (vi) Other Covenants. Guarantor will throughout the Term of
the Lease comply with all covenants of Guarantor contained in Section 9 of the
Credit Agreement, all of which are incorporated herein by reference; provided,
however, to the extent that any such covenant is inconsistent with any covenant
in the Operative Documents, including, without limitation contained in this
subparagraph (a), such covenant in the Operative Documents shall control and
shall not be subject to (b) below.

            (b) The covenants incorporated by reference in (a)(vi) above, and
the related definitions shall, without further action hereunder, be amended to
conform to any amendment, written waiver, or modification to such covenants (or
related definitions) contained in the Credit Agreement; provided however, that
if the Credit Agreement shall be terminated for any reason, the form of the
covenants and the related definitions incorporated by reference in (a)(vi) above
at the time of such termination shall continue hereunder and Guarantor shall
execute such amendments or supplements hereto evidencing such survival as the
Agent Bank may reasonably request.

            (c) As used in this paragraph 10, the following terms shall have the
following meanings:

            "Acquired Debt" shall mean, with respect to the Guarantor or any
Subsidiary, Indebtedness of any other Person, existing at the time such other
Person merged with or into or became a Subsidiary of the Guarantor or any
Subsidiary thereof in connection with a Permitted Acquisition, provided that (i)
such Indebtedness was not created by such other Person in contemplation of such
acquisition and (ii) the aggregate outstanding principal amount of such
Indebtedness shall not at any time exceed $7,500,000.

<PAGE>
                                       15


            "Acquisition" shall mean an acquisition of assets of, or all or
substantially all of the Capital Stock of, another business by Guarantor and/or
one or more of its Subsidiaries.

            "Acquisition Consideration" shall mean, with respect to any
Acquisition, the aggregate amount of consideration paid by Guarantor and its
Subsidiaries in connection therewith, inclusive of (a) Stock Consideration and
(b) other consideration on account of (i) any expenses incurred in connection
with such Acquisition, (ii) liabilities under agreements not to compete incurred
in connection with such Acquisition, (iii) the principal amount of Indebtedness
assumed in connection with such Acquisition and (iv) Additional Expenditures
related to such Acquisition.

            "Additional Expenditures" shall mean, with respect to any
Acquisition, amounts expended or to be expended by Guarantor and its
Subsidiaries within twelve months after the date of such Acquisition to acquire
or construct facilities and equipment that are not part of the assets acquired
pursuant to such Acquisition but which are deemed by Guarantor to be essential
for the integration or restructuring of the assets so acquired.

            "Adjusted EBITDA" shall mean, for any period, EBITDA for such
period, minus the tax provision for such period currently payable.

            "Arcus UK" shall mean Arcus Data Security Limited, an English
company that, prior to the formation of the Pond Joint Venture, was wholly owned
by Arcus Data Security, Inc., a Delaware corporation and Wholly Owned Subsidiary
of the Guarantor.

            "Capital Expenditures" shall mean expenditures in respect of fixed
assets by Guarantor or any of its Subsidiaries, including the capitalized amount
of Capital Lease Obligations incurred during the relevant period, other than (i)
expenditures for the restoration or

<PAGE>
                                       16


replacement of fixed assets to the extent financed by the proceeds of an
insurance policy described in clause (i) of Section 9.03 of the Credit Agreement
or through a condemnation award, (ii) Permitted Acquisitions, (iii) Qualifying
Sale-Leaseback Transactions (except to the extent any lease of property or
assets by Guarantor or any of its Subsidiaries in connection therewith would
constitute a capital lease), (iv) Additional Expenditures related to Permitted
Acquisitions and (v) Large Volume Account Capitalized Expenditures.

            "Capital Lease Obligations" shall mean, as to any Person, the
obligations of such Person to pay rent or other amounts under a lease of (or
other agreement conveying the right to use) real and/or personal property which
obligations are required to be classified and accounted for as a capital lease
on a balance sheet of such Person under GAAP (including Statement of Financial
Accounting Standards No. 13 of the Financial Accounting Standards Board) and,
for purpose of this Agreement, the amount of such obligations shall be the
capitalized amount thereof, determined in accordance with GAAP (including such
Statement No. 13).

            "Dollars" and "$" shall mean lawful money of the United States of
America.

            "EBITDA" shall mean for any period, the sum (without duplication),
determined on a consolidated basis for Guarantor and its Subsidiaries, of (a)
net income for such period plus (b) to the extent deducted in determining net
income for such period, the sum of (i) depreciation and amortization (including
deferred financing costs, organization costs, goodwill and non-compete
amortization) for such period, (ii) other non-cash expenses for such period,
(iii)Interest Expense for such period, (iv) provision for income taxes for such
period, (v) extraordinary losses (including without limitation losses arising
from any natural disasters) for such period, (vi) non-compete expenses for such
period to the extent not capitalized in accordance with GAAP and (vii) losses on
sales of fixed assets not in the ordinary course of business for such period
after giving effect to any related charges for, reductions of or provisions for
taxes thereon minus (c) to

<PAGE>
                                       17


the extent included in the calculation of net income for such period, the sum of
(i) other income (including interest income) for such period, (ii) extraordinary
gains for such period and (iii) gains on sales of fixed assets not in the
ordinary course of business for such period after giving effect to any related
charges for, reduction of or provisions for taxes thereon.

            For the purposes of calculating the ratios set forth in clauses
(i)(A), (ii) and (iii) of paragraph 10(a) there may, at the Guarantor's option,
and for purposes of calculating the ratio set forth in clause (i)(B) of
paragraph 10(a) there will be included in EBITDA for any relevant period, on a
pro forma basis (adjusted to give effect to expenses that will not be ongoing),
the net income (and the additions and subtractions thereto referred to above)
for such period of any Person (or assets) acquired after the commencement of
such period in connection with any acquisition not prohibited hereunder or under
the Credit Agreement where the aggregate amount of consideration paid is more
than $500,000. The net income (and the related additions and subtractions) of
the Person or assets acquired pursuant to such acquisition for such period shall
be calculated by reference to the most recent available quarterly financial
statement of the acquired business, annualized.

            "Excluded Subsidiary" shall mean any Subsidiary of the Guarantor
principally engaged in the records management business organized outside the
United States.

            "Fixed Charges" shall mean for any period the sum of (i) Scheduled
Amortization for such period plus (ii) Interest Expense for such period plus
(iii) the aggregate amount of Maintenance Capital Expenditures for such period
plus (iv) the aggregate amount of non-compete expenses for such period to the
extent not capitalized in accordance with GAAP.

            "Foreign Leverage Ratio" has the meaning set forth in Section
10(a)(i)(B)(ii) hereof.

<PAGE>
                                       18


            "Funded Indebtedness" shall mean, without duplication, (a)
Indebtedness (other than in respect of Synthetic Lease Obligations) that matures
or otherwise becomes due more than one year after the incurrence thereof or is
extendible, renewable or refundable, at the option of the obligor, to a date
more than one year after the incurrence thereof (including the current portion
thereof), (b) Indebtedness outstanding under the Credit Agreement and (c)
Synthetic Lease Obligations of Lessee and any Guarantees by the Guarantor
thereof.

            "GAAP" shall mean generally accepted accounting principles as in
effect from time to time consistently applied.

            "Guaranty" by any Person means any obligation, contingent or
otherwise, of such Person directly or indirectly guaranteeing any Indebtedness
of any other Person and, without limiting the generality of the foregoing, any
obligation, direct or indirect, contingent or otherwise, of such Person (i) to
purchase or pay (or advance or supply funds for the purchase or payment of) such
Indebtedness (whether arising by virtue of partnership arrangements, by
agreement to keep-well, to purchase assets, goods, securities or services, to
take-or-pay, or to maintain financial statement conditions or otherwise, other
than agreements to purchase goods at an arm's length price in the ordinary
course of business) or (ii) entered into for the purpose of assuring in any
other manner the holder of such Indebtedness of the payment thereof or to
protect such holder against loss in respect thereof (in whole or in part),
provided that the term Guaranty shall not include endorsements for collection or
deposit in the ordinary course of business. The term "Guarantee" used as a verb
has a corresponding meaning.

            "Indebtedness" shall mean, as to any Person (determined without
duplication):

            (i) indebtedness of such Person for borrowed money (whether by loan
      or the issuance and sale of debt securities) or for the deferred purchase
      or acquisition price of

<PAGE>
                                       19


      property or services (including amounts payable under agreements not to
      compete and other similar arrangements), other than accounts payable
      (other than for borrowed money) incurred in the ordinary course of
      business and accrued expenses incurred in the ordinary course of business;

            (ii) obligations of such Person in respect of letters of credit or
      similar instruments issued or accepted by banks and other financial
      institutions for the account of such Person;

            (iii) Capital Lease Obligations and Synthetic Lease Obligations of
      such Person;

            (iv) obligations of such Person to redeem or otherwise retire shares
      of Capital Stock of such Person;

            (v) indebtedness of others of the type described in clauses (i)
      through (iv) above secured by a Lien on the property of such Person,
      whether or not the respective obligation so secured has been assumed by
      such Person; and

            (vi) indebtedness of others of the type described in clause (i)
      through (v) above Guaranteed by such Person.

Notwithstanding anything to the contrary contained in clause (i) of the
preceding sentence, indebtedness of any Person in respect of amounts payable
under an agreement not to compete shall be the amount carried on the balance
sheet of such Person in respect of such agreement in accordance with GAAP.

<PAGE>
                                       20


            "Interest Expense" shall mean, for any period, the sum (determined
without duplication) of the aggregate amount of interest accruing during such
period on Indebtedness of the Guarantor and its Subsidiaries (on a consolidated
basis), including the interest portion of rental or similar payments under
Capital Lease Obligations and Synthetic Leases and any capitalized interest, and
excluding amortization of debt discount and expense and interest paid in kind.

            "Large Volume Account Capitalized Expenditures" shall mean any
expenditures incurred by Guarantor or its Subsidiaries in connection with new
customers initially storing with Guarantor or its Subsidiaries in excess of
10,000 boxes, to the extent that such expenditures are capitalized in accordance
with GAAP.

            "Lender" shall have the meaning assigned to such term in the Credit
Agreement.

            "Leverage Ratio" has the meaning set forth in Section
10(a)(i)(A)(ii) hereof.

            "Lien" shall mean, with respect to any asset, any mortgage, lien,
pledge, charge, security interest or encumbrance of any kind in respect of such
asset. For the purposes of this paragraph 10, Guarantor and each of its
Subsidiaries shall be deemed to own subject to a Lien any asset which it has
acquired or holds subject to the interest of a vendor or lessor under any
conditional sale agreement, capital lease or other title retention agreement
relating to such asset.

            "Liquid Investments" shall mean:

            (i) certificates of deposit maturing within 90 days of the
      acquisition thereof denominated in Dollars and issued by (X) a Lender or
      (Y) a bank or trust company having combined capital and surplus of at
      least $500,000,000 and which has (or which is

<PAGE>
                                       21


      a Subsidiary of a bank holding company which has) publicly traded debt
      securities rated A or higher by Standard & Poor's Ratings Services or A-2
      or higher by Moody's Investors Service, Inc.;

            (ii) repurchase obligations with a term of not more than seven days
      for underlying securities of the types described in clause (i) above
      entered into with (x) any Lender or (y) any bank or trust company meeting
      the qualifications specified in clause (i)(Y) above;

            (iii) obligations issued or guaranteed by the United States of
      America, with maturities not more than one year after the date of issue;

            (iv) commercial paper with maturities of not more than 90 days and a
      publishing rating of not less than A-2 and P-2 (or the equivalent rating);
      and

            (v) investments in money market funds substantially all of whose
      assets are comprised of securities and other obligations of the types
      described in clauses (i) through (iv) above.

            "Maintenance Capital Expenditures" shall mean Capital Expenditures
required to maintain, reconfigure, or replace existing assets (as distinguished
from Capital Expenditures relating to growth and as distinguished from
Additional Expenditures), as certified consistent with the provisions of Section
9.01(i) of the Credit Agreement.

            "Permitted Acquisition" has the meaning set forth in Section 9.12 of
the Credit Agreement.

<PAGE>
                                       22


            "Permitted Indebtedness" shall have the meaning assigned to such
term in the Credit Agreement.

            "Permitted Investment" shall have the meaning assigned to such term
in the Credit Agreement.

            "Person" shall mean an individual, a corporation, a company, a
voluntary association, a partnership, a limited liability company, a trust, an
unincorporated organization or a government agency or any agency,
instrumentality or political subdivision thereof.

            "Pond Joint Venture" shall mean Britannia Data Management Limited,
an English company, a majority of the shares of Capital Stock of which
(immediately after giving effect to the Pond Transaction) will be owned by the
Guarantor or a Subsidiary of the Guarantor.

            "Pond Transaction" shall mean (i) the contribution by the Guarantor
or a Subsidiary of the Guarantor to the Pond Joint Venture of Capital Stock of
Arcus UK having a fair market value of up to but not exceeding (pound)2,000,000
and (ii) the purchase by the Guarantor or a Subsidiary of the Guarantor of
Capital Stock of the Pond Joint Venture for an aggregate consideration of up to
but not exceeding (pound)37,250,000.

            "Qualifying Sale-Leaseback Transaction" shall mean any arrangement
by which Guarantor or any of its Subsidiaries enters into an arrangement with
any bank, insurance company or other lender or investor providing for the
leasing to Guarantor or a Subsidiary thereof of any real property which has been
or is to be sold or transferred by Guarantor or such Subsidiary to such lender
or investor or to any Person to whom funds have been or are to be advanced by
such lender or investor and where the real property in question has been
constructed after September 26, 1997.

<PAGE>
                                       23


            "Scheduled Amortization" shall mean, for any period, the sum
(calculated without duplication) of all payments of principal of Indebtedness of
Guarantor (other than Indebtedness under the Credit Agreement) scheduled to be
made during such period.

            "Security Documents" shall have the meaning assigned to such term in
the Credit Agreement.

            "Stock Consideration" shall mean, with respect to any Acquisition,
the aggregate amount of consideration paid by Guarantor and its Subsidiaries in
connection therewith consisting of Guarantor's common stock or with proceeds of
the issuance of Guarantor's common stock within twelve months prior to the date
of such Acquisition. For purposes hereof, the amount of Stock Consideration paid
by Guarantor in respect of any Acquisition where the Stock Consideration
consists of Guarantor's common stock shall be deemed to be equal to the fair
market value of Guarantor's common stock so paid, determined in good faith by
Guarantor at the time of such Acquisition.

            "Subsidiary" shall mean, with respect to any Person, any
corporation, partnership, limited liability company or other entity of which at
least a majority of the securities or other ownership interests having by the
terms thereof ordinary voting power to elect a majority of the board of
directors or other persons performing similar functions of such corporation,
partnership, limited liability company or other entity (irrespective of whether
or not at the time securities or other ownership interests of any other class or
classes of such corporation, partnership, limited liability company or other
entity shall have or might have voting power by reason of the happening of any
contingency) is at the time directly or indirectly owned or controlled by such
Person or one or more Subsidiaries of such Person or by such Person and one or
more Subsidiaries of such Person.

<PAGE>
                                       24


            "Synthetic Lease" shall mean a lease of property or assets designed
to permit the lessee (i) to claim depreciation on such property or assets under
U.S. tax law and (ii) to treat such lease as an operating lease or not to
reflect the leased property or assets on the lessee's balance sheet under GAAP.

            "Synthetic Lease Obligations" shall mean, with respect to any
Synthetic Lease, at any time, an amount equal to the higher of (x) the aggregate
termination value or purchase price or similar payments in the nature of
principal payable thereunder and (y) the then aggregate outstanding principal
amount of the notes or other instruments issued by, and the amount of the equity
investment, if any, in the lessor under such Synthetic Lease.

            (d)(x) Guarantor shall not merge into or consolidate with any other
Person or sell, transfer, lease or otherwise convey all or substantially all its
assets as an entirety; provided that, so long as no Default or Event of Default
shall have occurred and be continuing or would result therefrom, the Guarantor
may merge with another Person so long as (i) the Guarantor is the surviving
entity, and (ii) after giving effect to such merger, the Guarantor, as the
surviving entity, would have a tangible net worth (as hereinafter defined) equal
to or greater than Guarantor's tangible net worth immediately prior to such
merger.

            (y) Guarantor shall not permit any of its Subsidiaries to merge into
or consolidate with any other Person or sell, transfer, lease or otherwise
convey all or substantially all their assets as an entirety; provided that (a)
Lessee may merge into or consolidate with any other Person or sell, transfer,
lease or otherwise convey all or substantially all its assets as an entirety in
accordance with Article 15 of the Lease and (b) so long as no Default or Event
of Default shall have occurred and be continuing or would result therefrom, that
(A) any Subsidiary may sell, transfer, lease or otherwise convey all or
substantially all of its assets to the Guarantor or any Person that is, or
becomes, a Subsidiary of the Guarantor or (B) any Subsidiary may merge into

<PAGE>
                                       25


the Guarantor or any of its Subsidiaries, and (C) any Subsidiary (other than
Lessee) may merge into another Person if, contemporaneously therewith, such
Person becomes a Subsidiary of the Guarantor.

            (z) The Guarantor shall not, and shall not permit any of its
Subsidiaries to, issue or sell any stock of any Subsidiary that is not an
Excluded Subsidiary to any Person or Persons, other than to the Guarantor or its
Subsidiaries, to the extent not prohibited by clause (x) of this subparagraph
(d) above.

      "tangible net worth" of the Guarantor means, at any date, the excess of
the consolidated total assets of Guarantor and its Subsidiaries at such date
over the consolidated total liabilities of Guarantor and its Subsidiaries at
such date, and less (without duplication of amounts) the sum at such date of :
(i) all goodwill, organizational expenses, research and development expenses,
trademarks, trade names, copyrights, patents, patent applications, licenses and
rights in any thereof, and other similar intangibles, (ii) all reserves carried
and not deducted from assets or included in consolidated total liabilities,
(iii) securities which are not readily marketable, (iv) any subscriptions
receivable and (v) any items not included in clauses (i) through (iii) above,
which are treated as intangibles in conformity with GAAP, all of the foregoing
as determined for any such date as of the end of the immediately preceding
fiscal quarter in accordance with GAAP.

      (e) Guarantor shall at all times during the Term of the Lease carry a
footnote on its financial statements required by paragraph 9 hereof referring to
the transactions contemplated by the Operative Documents, in the form currently
appearing in Guarantor's financial statements.

      (f) Unless otherwise specified herein, all accounting terms used herein
shall be interpreted, all determinations with respect to accounting matters
hereunder shall be made, and all financial statements and certificates and
reports as to financial matters required to be

<PAGE>
                                       26


delivered hereunder shall be prepared, in accordance with GAAP; provided that if
any change in GAAP proposed after the date hereof in itself materially affects
the calculation of any financial covenant in this paragraph 10 (or incorporated
by reference herein), the Guarantor may by notice to the Owner and Agent Bank,
or the Owner or Agent Bank may by notice to the Guarantor, require that such
covenant thereafter be calculated in accordance with GAAP as in effect, and
applied by the Guarantor, immediately before such change in GAAP occurs.

      11. Guarantor will permit Owner and the Indemnified Parties to visit the
offices of Guarantor at its address set forth herein and to examine its records
and books of account and to discuss its affairs, finances and accounts with its
officers upon reasonable notice at such reasonable times as may be requested by
Owner or such Indemnified Party or any assignee of Owner's rights hereunder.

      12. Guarantor understands and acknowledges that Owner may enter into one
or more financings to finance the Costs of the Properties pursuant to which
Owner will encumber its interest in the Properties. In connection with any such
financing, Guarantor understands and acknowledges that Owner may assign its
rights in and to this Guaranty and Guarantor hereby agrees that: (i) Owner may
assign its rights hereunder in connection therewith; (ii) in connection with any
such assignment by Owner, Guarantor will consent in writing thereto; and (iii)
from and after such assignment, the rights and benefits of Owner hereunder shall
inure to the benefit of, and be exercisable by any assignee, pursuant to and in
accordance with the terms of such assignment.

      13. Guarantor agrees that at any time and from time to time so long as
this Guaranty is in effect, it will promptly, but in no event later than 15 days
after request by Owner, execute, acknowledge and deliver to Owner a certificate
stating: (i) that this Guaranty is unmodified and in full force and effect (or
if there have been modifications, that this Guaranty is in full force and effect
as modified, and identifying such modification agreements); (ii) whether or not
there is an

<PAGE>
                                       27


existing Default or Event of Default hereunder and, if there is any such Default
or Event of Default, specifying the nature and extent thereof; and (iii) whether
or not there are any setoffs, defenses or counterclaims against enforcement of
the obligations to be performed hereunder existing in favor of Guarantor.
Guarantor further agrees that it will upon five day's prior notice from Owner
execute and deliver to Owner's mortgagee a certificate stating the above.

      14. Guarantor represents and warrants that:

            (a)   Guarantor (i) is a corporation duly organized and validly
                  existing under the laws of the State of Delaware, and (ii) has
                  all requisite legal power and authority to enter into this
                  Guaranty, to perform and observe the terms and conditions
                  hereof, and has all requisite legal power and authority to own
                  its properties and conduct its business as currently conducted
                  except for such licenses, permits and approvals which would
                  not, individually or in the aggregate, have a material adverse
                  effect on Guarantor's ability to perform the Guaranteed
                  Obligations. Guarantor is qualified to do business as a
                  foreign corporation in all jurisdictions where its ownership
                  of property or the nature of its business required such
                  qualification. This Guaranty has been duly authorized,
                  executed and delivered by Guarantor and constitutes the legal,
                  valid and binding obligation by Guarantor enforceable against
                  Guarantor in accordance with its terms, except as enforcement
                  may be limited by bankruptcy, insolvency, reorganization and
                  other laws of general application relating to or affecting the
                  enforcement of creditors' rights and general principles of
                  equity.

            (b)   There are no actions, suits or proceedings pending or, to its
                  actual knowledge, threatened against or affecting Guarantor at
                  law or in equity before any court or administrative office or
                  agency an adverse determination in which could, individually
                  or in the aggregate, have a material adverse effect on
                  Guarantor's ability to perform the Guaranteed Obligations.
                  Guarantor is not in default (i) in the payment of any taxes
                  levied or assessed against it or its assets or (ii) under or
                  in violation of any statute, rule, order, decree, writ,
                  injunction or regulation of any governmental body (including
                  any court) except where the failure to pay such taxes or the
                  existence of such defaults or violations would, individually
                  or in the aggregate, not have a material adverse effect on
                  Guarantor's ability to perform the Guaranteed Obligations.

<PAGE>
                                       28


            (c)   Guarantor is not a party to any contract or agreement or
                  subject to any restriction or to any order, rule, regulation,
                  writ, injunction or decree of any court or governmental
                  authority or to any statue which materially and adversely
                  affects its ability to perform the Guaranteed Obligations.
                  Neither the execution, delivery or performance by Guarantor of
                  this Guaranty nor its compliance herewith or therewith (i)
                  conflicts or will conflict with or results or will result in a
                  breach of or constitutes or will constitute a default under
                  (A) any law in effect as of the date of delivery of this
                  Guaranty, (B) the articles of incorporation or by-laws of
                  Guarantor, (C) any agreement or instrument to which Guarantor
                  is a party or by which it is bound, or (D) any order, writ,
                  injunction or decree of any court or other governmental
                  authority, or (ii) results or will result in the creation or
                  imposition of any lien, charge or encumbrance upon Guarantor's
                  property pursuant to such agreement or instrument.

            (d)   The execution, delivery and performance by Guarantor of this
                  Guaranty do not require (i) any stockholder approval or the
                  consent or approval of any of Guarantor's creditors (except as
                  have already been obtained in writing), or (ii) any
                  authorization, consents, or approvals, of or filings with any
                  governmental authority, except for such authorization,
                  consents, approvals or filings which have been obtained and
                  are in full force and effect.

            (e)   No event has occurred and is continuing with respect to
                  Guarantor which would constitute a Default or an Event of
                  Default hereunder. No Default or Event of Default by Lessee
                  exists under the Agency Agreement or the Lease. Guarantor is
                  not in default in the payment of the principal or interest on
                  any indebtedness for borrowed money or for its deferred
                  purchase of property or in default under any instrument or
                  agreement under and subject to which any such indebtedness has
                  been issued or under any lease, in any case involving the
                  likelihood of any actions or proceedings against it which
                  would materially and adversely affect Guarantor or its ability
                  to perform under this Guaranty.

            (f)   Guarantor is in compliance in all material respects with all
                  applicable provisions of the Employee Retirement Income
                  Security Act of 1974, as amended (ERISA), and the regulations
                  and published interpretations thereunder. No "reportable
                  event", as such term is defined in Section 4043 of ERISA, has
                  occurred with respect to any employee pension benefit plan (as
                  defined in ERISA), and Guarantor has not incurred, nor does it
                  reasonably expect to incur, any liability to the Pension
                  Benefit Guaranty

<PAGE>
                                       29


                  Corporation under Section 44062 of ERISA or to any
                  multiemployer plan (as defined in ERISA) under Section 4201 of
                  ERISA. Guarantor has not incurred any accumulated funding
                  deficiency within the meaning of Section 302 of ERISA nor is
                  it subject to any lien arising under Section 307 of ERISA or
                  Section 401(a)(29) or 412(n) of the Internal Revenue Code of
                  1986, as amended.

            (g)   Guarantor's assets are not less than its liabilities, both
                  determined in accordance with GAAP, and Guarantor is solvent.
                  The transactions contemplated by this Guaranty are in
                  furtherance of Guarantor's ordinary business purposes and in
                  furtherance of its corporate purposes with no contemplation of
                  insolvency and with no intent to hinder, delay or defraud any
                  of its present or future creditors. Neither before nor as a
                  result of the transactions contemplated by this Guaranty will
                  Guarantor be or be rendered insolvent or have an unreasonably
                  small capital for the conduct of its business and the payment
                  of its anticipated obligations. Guarantor's assets and cash
                  flow enable it to meet its present obligations in the ordinary
                  course of business as they become due, and Guarantor does not
                  believe that it will incur debts beyond its ability to pay
                  such debts.

            (h)   Neither (i) the consolidated financial statements for
                  Guarantor's fiscal year ending in December 31, 1998, (ii) this
                  Guaranty, nor (iii) any written statement furnished by
                  Guarantor in connection with the transactions contemplated by
                  the Operative Documents, contains any untrue statement of a
                  material fact or omits a material fact necessary to make the
                  statements contained therein not misleading. There is no fact
                  applicable to Guarantor which Guarantor has not disclosed in
                  writing which materially affects adversely nor so far as
                  Guarantor can now reasonably foresee will materially affect
                  adversely the properties, business, prospects, profits or
                  condition (financial or otherwise) of Guarantor. Guarantor
                  represents that the consolidated financial statements
                  specified above (i) are complete and correct in all material
                  respects, (ii) present fairly in all material respects the
                  financial condition of Guarantor on the dates for which, and
                  the results of its operations for the periods for which, the
                  same have been furnished, and (iii) have been prepared in
                  accordance with GAAP consistently applied, except as otherwise
                  disclosed therein. Guarantor represents that as of the Initial
                  Closing Date there shall have been no material adverse change
                  in the condition of Lessee, financial or otherwise, since the
                  date of the most recent financial statements of Guarantor
                  delivered to Owner.

<PAGE>
                                       30


            (i)   There has been no material adverse change in Guarantor's
                  business or financial condition since December 31, 1998 that
                  individually or the aggregate would adversely affect
                  Guarantor's ability to perform the Guaranteed Obligations.

      15. All agreements, representations and warranties contained herein or
made in writing by Guarantor shall survive the execution and delivery of this
Guaranty.

      16. This Guaranty shall be binding upon, and inure to the benefit of, the
parties hereto and their respective successors and assigns.

      17. This Guaranty shall be construed and enforced in accordance with, and
governed by, the laws of the Commonwealth of Massachusetts. In connection with
this Guaranty and the transactions contemplated by the Operative Documents,
Guarantor hereby agrees to the non-exclusive personal jurisdiction of and venue
in the state courts of the Commonwealth of Massachusetts, and the United States
District Courts located in the Commonwealth of Massachusetts.

      18. Any provision of this Guaranty which is prohibited or unenforceable in
any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of
such prohibition or unenforceability without invalidating the remaining
provisions hereof, and any such prohibition or unenforceability in any
jurisdiction shall not invalidate or render unenforceable such provision in any
other jurisdiction.

      19. Any notice to be given under this Guaranty shall be given in the
manner provided in the Lease, addressed to Guarantor or Owner at its address set
forth at the beginning of this Guaranty, or as either such party may otherwise
provide by notice to the other party.

      20. GUARANTOR HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED
BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING
ARISING OUT OF OR RELATING TO THIS GUARANTY OR THE TRANSACTIONS CONTEMPLATED
HEREBY. THIS WAIVER IS KNOWINGLY, INTENTIONALLY AND VOLUNTARILY MADE BY
GUARANTOR; AND GUARANTOR FURTHER ACKNOWLEDGES THAT IT HAS

<PAGE>
                                       31


BEEN REPRESENTED (OR HAS HAD THE OPPORTUNITY TO BE REPRESENTED) IN THE SIGNING
OF THIS GUARANTY AND IN THE MAKING OF THIS WAIVER BY INDEPENDENT LEGAL COUNSEL,
SELECTED OF ITS OWN FREE WILL, AND THAT IT HAS HAD THE OPPORTUNITY TO DISCUSS
THIS WAIVER WITH COUNSEL.


                                       ***

<PAGE>

      IN WITNESS WHEREOF, Guarantor has caused this Unconditional Guaranty to be
executed under seal and delivered as of the day and year first above written.

                                          IRON MOUNTAIN INCORPORATED


                                          By:   /s/ J. P. Lawrence
                                                ----------------------------
                                                Name: J.P. Lawrence
                                                Title:  VP, Treasurer