<Page>

                                  EXHIBIT 10.4


                            SECOND AMENDMENT TO LEASE

         THIS SECOND AMENDMENT TO LEASE ("SECOND AMENDMENT") is made and
entered into as of the 8th day of March, 2001, by and between LBA OVERLAND,
LLC, a California limited liability company ("LANDLORD") and OVERLAND DATA,
INC., a California corporation ("TENANT").

                                R E C I T A L S:
                                - - - - - - - -

         A. LBA-VIF ONE, LLC, a California limited liability company
("LBA-VIF ONE") and Tenant entered into that certain Build-To-Suit
Single-Tenant Lease (Triple Net) dated as of October 12, 2000 ("ORIGINAL
LEASE"), as amended by that certain First Amendment to Lease dated January
18, 2001 ("FIRST AMENDMENT") whereby LBA-VIF One leased to Tenant and Tenant
leased from LBA-VIF One those certain Premises located in the City of San
Diego, County of San Diego, all as more particularly described in the Lease.
The Original Lease, as amended by the First Amendment, may be referred to
herein as the "LEASE." Landlord is successor-in-interest in the Lease to
LBA-VIF One.

         B. By this Second Amendment, Landlord and Tenant desire to amend the
Lease to (i) restate Landlord's and Tenant's obligations pertaining to the
Other Lease (as described below), and (ii) otherwise modify the Lease as
provided herein.

         C. Unless otherwise defined herein, capitalized terms as used herein
shall have the same meanings as given thereto in the Lease.

         NOW, THEREFORE, in consideration of the foregoing recitals and the
mutual covenants contained herein, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged,
the parties hereto hereby agree as follows:

                               A G R E E M E N T:
                               - - - - - - - - -

         1. RESTATEMENT OF "OTHER LEASE" PROVISIONS. Effective as of the date
hereof, Landlord and Tenant acknowledge and agree that Section 33 of the
Lease is deemed deleted in its entirety and replaced with the following:

                  "33. OTHER LEASE.

                           33.1 TERMINATION OF OTHER LEASE. Landlord and
Tenant acknowledge the existence of that certain other lease (as amended, the
"OTHER LEASE") dated May 26, 1993 executed by and between Tenant and
LBA-VFII, LLC a Delaware limited liability company, as successor-in-interest
in the Other Lease to Mitsui/SBD America Fund 87-1 (the "OTHER


                                      -1-
<Page>

LANDLORD") pursuant to which Other Lease, Tenant is leasing the following
buildings: (i) that certain building located at 8975 Balboa Avenue and
containing approximately 65,765 rentable square feet (the "8975 PREMISES"),
(ii) that certain building located at 8985 Balboa Avenue and containing
approximately 27,761 rentable square feet (the "8985 PREMISES"), and (iii)
that certain building located at 8965 Balboa Avenue and containing
approximately 27,761 rentable square feet (the "8965 PREMISES"). The 8975
Premises, the 8985 Premises and the 8965 Premises are collectively referred
to herein as the "OTHER PREMISES." The Other Landlord (by its execution
below) and Tenant acknowledge and agree that effective as of February 1,
2001, the Other Lease (pertaining to the entire second (2nd) floor portion of
the 8965 Premises (consisting of 13,881 rentable square feet) and 6,880
rentable square feet of the first (1st) floor portion of the 8965 Premises
only) was terminated; provided, however, that Tenant acknowledges and agrees
that Tenant shall continue to be liable under the Other Lease for (i) those
obligations under the Other Lease pertaining to the remaining portion of the
Other Premises and (ii) those obligations pertaining to the terminated
portions of the 8965 Premises that are intended to survive termination
including, without limitation, Tenant's indemnity obligations and Tenant's
reconciliation obligations for accrued operating expenses (that accrued prior
to February 1, 2001) under the Other Lease pertaining to the terminated
portions of the 8965 Premises, all of which obligations Tenant acknowledges
and agrees shall survive the expiration of the Other Lease pertaining to such
terminated portions of the 8965 Premises. The Other Landlord and Tenant
acknowledge and agree that effective as of February 1, 2001, the Other Lease
(as it pertains to the remaining portion of the first (1st) floor portion of
the 8965 Premises covered thereunder (which remaining portion is stipulated
by the parties to contain 7,000 rentable square feet)) shall be deemed
converted into a month-to-month tenancy, terminable by either party on thirty
(30) days prior written notice to the other, which month-to-month tenancy
shall be subject to all of the other terms and conditions of the Other Lease
(and such month-to-month tenancy shall not be deemed a holdover under such
Other Lease). Tenant shall, within ten (10) days of Other Landlord's written
request, execute a letter confirming the terms and conditions of such
month-to-month tenancy. On the Commencement Date of this Lease, the Other
Landlord and Tenant acknowledge and agree that the Other Lease shall be
terminated in its entirety (as to all of the remaining portion of the Other
Premises then being leased by Tenant); provided, however, that Tenant shall
continue to be liable under the Other Lease for those obligations under the
Other Lease that are intended to survive termination including, without
limitation, Tenant's indemnity obligations and Tenant's reconciliation
obligations for accrued operating expenses under the Other Lease (that
accrued prior to such termination date), all of which obligations Tenant
acknowledges and agrees will survive the expiration of the Other Lease.
Effective as of the date of the full execution and delivery of this Lease by
Landlord and Tenant, Tenant acknowledges and agrees that it shall provide
Landlord and Other Landlord with access to the remaining portion of the first
(1st) floor portion of the 8965 Premises in order for Landlord and/or the
Other Landlord to install an elevator and ancillary improvements in the 8965
Premises (collectively, the "WORK"). Tenant acknowledges and agrees that
Landlord's and/or the Other Landlord's performance of the Work shall not
entitle Tenant to any abatement of rent under the Other Lease nor will it
constitute a construction eviction of Tenant from the Other Premises.
Landlord and Other Landlord (by its execution below) acknowledges and agrees
that such Work shall be performed by Landlord and/or Other Landlord in a
manner so as to minimize any adverse interference with Tenant's business in
the remaining portions of the Other Premises. Landlord agrees to reimburse to
Tenant, up to Thirty


                                      -2-
<Page>

Thousand Dollars ($30,000.00) ("LANDLORD'S REIMBURSEMENT CAP") of the actual,
documented and reasonable moving costs incurred by Tenant in moving from the
second (2nd) floor portion of the 8965 Premises to the balance of the Other
Premises (and to other locations in San Diego County) within thirty (30) days
after Landlord's receipt of a reasonably particularized invoice evidencing
such costs.

                           33.2 ADDITIONAL MODIFICATIONS TO OTHER LEASE. By
its execution below, the Other Landlord and Tenant acknowledge and agree that
effective as of the date of the full execution and delivery of this Lease by
Landlord and Tenant, Paragraph 56 of the Addendum to the Other Lease
(pertaining to Tenant's renewal options) is hereby deemed deleted in its
entirety and shall be of no further force and effect whatsoever. The Other
Landlord and Tenant acknowledge and agree that the modifications to the Other
Lease set forth in this Section 33 shall survive the expiration or earlier
termination of this Lease."

         2. BROKERS. Each party represents and warrants to the other that no
broker, agent or finder negotiated or was instrumental in negotiating or
consummating this Second Amendment. Each party further agrees to defend,
indemnify and hold harmless the other party from and against any claim for
commission or finder's fee by any entity who claims or alleges that they were
retained or engaged by the first party or at the request of such party in
connection with this Second Amendment.

         3. DEFAULTS. Landlord and Tenant hereby represent and warrant to the
other that, as of the date of this Second Amendment, Landlord and Tenant, as
applicable, are in full compliance with all terms, covenants and conditions
of the Lease and that there are no breaches or defaults under the Lease by
Landlord or Tenant, and that neither party knows of no events or
circumstances which, given the passage of time, would constitute a default
under the Lease by either Landlord or Tenant.

         4. AUTHORITY. If either Landlord or Tenant executes this Second
Amendment as a limited liability company, partnership or corporation, then
such party and the persons and/or entities executing this Lease on behalf of
such party represents and warrants that: (a) it is a duly organized and
validly existing limited liability company, partnership or corporation, as
the case may be, and is qualified to do business in the state in which the
Premises are located; (b) such persons and/or entities executing this Second
Amendment are duly authorized to execute and deliver this Second Amendment on
such party's behalf in accordance with its operating agreement (if Landlord
or Tenant is a limited liability company), Landlord's or Tenant's partnership
agreement (if Landlord or Tenant is a partnership), or a duly adopted
resolution of Landlord's or Tenant's board of directors and its by-laws (if
Landlord or Tenant is a corporation); and (c) this Second Amendment is
binding upon Landlord and Tenant in accordance with its terms.

         5. NO FURTHER MODIFICATION. Except as set forth in this Second
Amendment, all of the terms and provisions of the Lease shall remain
unmodified and in full force and effect. Effective as of the date hereof, all
references to the "Lease" shall refer to the Lease as amended by this Second
Amendment.


                                      -3-
<Page>


         IN WITNESS WHEREOF, this Second Amendment has been executed as of
the day and year first above written.

"TENANT"                        OVERLAND DATA, INC.,
                                a California corporation


                                *By: /s/ Vernon A. LoForti
                                     -------------------------------------------
                                     Name:  Vernon A. LoForti
                                     Title:  Vice President and Chief Financial
                                             Officer


                                By:  /s/  Scott McClendon
                                     -------------------------------------------
                                     Name:  Scott McClendon
                                     Title:  President and Chief Executive
                                             Officer

"LANDLORD"                      LBA OVERLAND, LLC,
                                a California limited liability company

                                By:  Spectrum Overland, L.P., a California
                                     limited partnership, its Member-Manager

                                     By:  LBA Fund I, Inc., a California
                                          corporation, its General Partner


                                          By:  /s/ Phil A. Belling
                                              ---------------------------
                                              Name: Phil A. Belling
                                                   ----------------------
                                              Title: Authorized Signatory
                                                    ---------------------









--------
*NOTE:

IF TENANT IS A CALIFORNIA CORPORATION, then one of the following alternative
requirements must be satisfied:
(A)      This Lease must be signed by two (2) officers of such corporation: one
         being the chairman of the board, the president or a vice president, AND
         the other being the secretary, an assistant secretary, the chief
         financial officer or an assistant treasurer. If one (1) individual is
         signing in two (2) of the foregoing capacities, that individual must
         sign twice; once as one officer and again as the other officer.
(B)      If there is only one (1) individual signing in two (2) capacities, or
         if the two (2) signatories do not satisfy the requirements of (A)
         above, then Tenant shall deliver to Landlord a certified copy of a
         corporate resolution in the form reasonably acceptable to Landlord
         authorizing the signatory(ies) to execute this Lease.
IF TENANT IS A CORPORATION INCORPORATED IN A STATE OTHER THAN CALIFORNIA, then
Tenant shall deliver to Landlord a certified copy of a corporate resolution in
the form reasonably acceptable to Landlord authorizing the signatory(ies) to
execute this Lease.


                                      -4-
<Page>




                        ACKNOWLEDGMENT OF OTHER LANDLORD



         By its execution below, Other Landlord hereby consents to the
modification to the Lease set forth in the foregoing Second Amendment.

"OTHER LANDLORD"              LBA-VFI, LLC,
                              a California limited liability company

                              By: LBA, Inc., a California corporation, its agent


                                  By: /s/ Phil A. Belling
                                      ------------------------------------------
                                      Name: Phil A. Belling
                                            ------------------------------------
                                      Title: Authorized Signatory
                                             -----------------------------------


                                      -5-