Exhibit 10.19.4

MCDATA SYNTHETIC LEASE  SECOND AMENDMENT TO PARTICIPATION AGREEMENT

This SECOND AMENDMENT TO PARTICIPATION AGREEMENT (this "Amendment") dated as of November 9, 2001, is by
and among MCDATA CORPORATION, a Delaware corporation, as Lessee and Construction Agent (in its capacity as Lessee, the "Lessee" and in its capacity as
Construction Agent, the "Construction Agent"); DEUTSCHE BANK AG, NEW YORK BRANCH, a duly licensed branch of Deutsche Bank AG, a German corporation, as
Agent Lessor for the Lessors (in such capacity, the "Agent Lessor"), and as a Lessor (together with any permitted successors and assigns, each a
"Lessor" and collectively the "Lessors"); and DEUTSCHE BANK AG, NEW YORK AND/OR CAYMAN ISLANDS BRANCH,
as a Lender (together with the other financial institutions as may from time to time become lenders, the "Lenders") under the Credit Agreement and as
Agent for the Lenders (in such capacity, the "Agent"). Capitalized terms used herein and not otherwise defined shall have the meanings assigned such
terms in Annex A to the Participation Agreement (as defined below).

RECITALS:

A.  The
Lessee, the Agent Lessor, the Lessor, the Lender, the Agent and the Arranger are parties to that certain Participation Agreement, dated as of February 9,
2001 (as amended, restated, supplemented or otherwise modified from time to time, the "Participation Agreement").

B.  Section 9.5(g) of
the Participation Agreement contains a covenant of the Lessee to maintain at all times a minimum Consolidated Fixed Charge Coverage
Ratio. In the Lessee's third fiscal quarter of 2001, the Lessee booked one-time charges relating to: a write down of excess and obsolete inventory; SANavigator, Inc.
one-time acquisition charges; and SANavigator, Inc. one time in-process allocation charges.

C.  The
Lessee has requested certain amendments to the Participation Agreement to recognize the effect of certain of these charges.

D.  The
parties signatory hereto are willing to agree to those amendments on the terms, and subject to the conditions, hereinafter set forth.

NOW,
THEREFORE, in consideration of the premises and the mutual covenants hereinafter contained, the parties hereto agree as follows:

1.Amendment to Annex A to the Participation Agreement.Subject to the satisfaction of the conditions set forth in Section 5below, Annex A to the Participation
Agreement is hereby amended as follows:



2.Amendment to the Participation Agreement.Subject to satisfaction of the conditions set forth in Section 5below, Section 9.5(g) of the Participation
Agreement is hereby amended by deleting the same in its entirety and replacing it
with the following:



Period

RatioClosing Date through 9/30/01

2.0:1.010/01/01 through 3/31/02

1.75:1.04/01/02 through 12/31/02

2.0:1.01/01/03 through 12/31/03

2.5:1.0Thereafter

3.0:1.0


3.Amendment to Exhibit K to the Participation Agreement.Subject to satisfaction of the conditions set forth in Section 5below, Exhibit K to the
Participation Agreement is hereby amended by deleting Annex A thereto in its entirety and replacing it
with Annex A attached hereto.

4.Representation and Warranties.The Lessee hereby represents and warrants to the Agent Lessor, the Lessor, the Lender
and the Agent that the following are true and correct on the date of this Amendment and that, after giving effect to the amendments set forth inSection 1above, the following will be true and
correct on the Effective Date (as defined below):



5.Effective Date.The amendments effected bySections 1, 2 and 3above shall become effective as of the date of September 30, 2001 (the "Effective Date"), subject to receipt by
McGuireWoods LLP, counsel to the Agent and the Agent Lessor, of a copy of this Amendment duly executed by the Lessee, the Agent Lessor, the Lessor, the Lender and the Agent.

6.Miscellaneous.



7.GOVERNING LAW.THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY AND
CONSTRUED, INTERPRETED AND ENFORCED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

IN
WITNESS WHEREOF, each party hereto has caused this Amendment to be duly executed and delivered by its proper and duly authorized officer as of the date first written above.

| |  | MCDATA CORPORATION,as Lessee and Construction Agent                                             
| |  | ------------------------------------------------------------------------------------------------
| |  | By:                                                                                             
| |  | Name:                                                                                           
| |  | Title:                                                                                          
| |  | DEUTSCHE BANK AG, NEW YORK BRANCH,as Agent Lessor for the Lessors and as a Lessor               
| |  | By:                                                                                             
| |  | Name:                                                                                           
| |  | Title:                                                                                          
| |  | By:                                                                                             
| |  | Name:                                                                                           
| |  | Title:                                                                                          
| |  | DEUTSCHE BANK AG, NEW YORK AND/OR CAYMAN ISLANDS BRANCH,as a Lender and as Agent for the Lenders
| |  | By:                                                                                             
| |  | Name:                                                                                           
| |  | Title:                                                                                          
| |  | By:                                                                                             
| |  | Name:                                                                                           
| |  | Title:                                                                                          



Annex A to Second Amendment to Participation Agreement

ANNEX A TO
COMPLIANCE CERTIFICATE

FOR THE FISCAL QUARTER ENDING ,($ in 000's)

|   |  |                                          |  |                                                                          |    |                                                                        |   | Calculation |     | Required
Ratio or Figure | 
|-- |  | ---------------------------------------- |  | ------------------------------------------------------------------------ | -- | ---------------------------------------------------------------------- | - | ----------- | --- | ------------------------ | 
|1. |  | Consolidated Tangible Net Worth (i)-(ii) |  |                                                                          |    |                                                                        |   |             |    
|   |  | (i)                                      |  | The sum of Consolidated Total Assets of the Lessee and its Subsidiaries; |    | $                                                                      |   |             |     |                          | 
|   |  | (ii)                                     |  | The sum of:                                                              |    | $                                                                      |   |             |     |                          | 
|   |  |                                          |  | (i)                                                                      |    | the Consolidated Total Liabilities of the Lessee and its Subsidiaries; |   | $           |     |                          | 
|   |  |                                          |  | (ii)                                                                     |    | all Intangible Assets of Lessee and its Subsidiaries.                  |   | $           |     |                          | 
|   |  | Consolidated Tangible Net Worth          |  | $                                                                        |    |                                                                        | $ | 200,000,000 |    
|2. |  | Consolidated Fixed Charge Ratio (i)/(ii) |  |                                                                          |    |                                                                        |   |             |    
|   |  | (a)                                      |  | the sum of                                                               |    |                                                                        |   |             |     |                          | 
|   |  |                                          |  | (i)                                                                      |    | Consolidated Net Income(1)                                             |   | $           |     |                          | 
|   |  |                                          |  | (ii)                                                                     |    | Consolidated Interest Expense                                          |   | $           |     |                          | 
|   |  |                                          |  | (iii)                                                                    |    | Consolidated Income Tax Expense                                        |   | $           |     |                          | 
|   |  |                                          |  | (iv)                                                                     |    | Consolidated Depreciation Expense                                      |   | $           |     |                          | 
|   |  |                                          |  | (v)                                                                      |    | Consolidated Lease Rental Expense                                      |   | $           |     |                          | 
|   |  | (b)                                      |  | the sum of                                                               |    |                                                                        |   |             |     |                          | 
|   |  |                                          |  | (i)                                                                      |    | CMLTD                                                                  |   | $           |     |                          | 
|   |  |                                          |  | (ii)                                                                     |    | Consolidated Interest Expense                                          |   | $           |     |                          | 
|   |  |                                          |  | (iii)                                                                    |    | Consolidated Lease Rental Expense                                      |   | $           |     |                          | 
|   |  | The Ratio                                |  |                                                                          | to |                                                                        |   | 2.0 to 1.0  | (2)
|   |  |                                          |  |                                                                          |    |                                                                        |   |             | to  |                          | 
|   |  |                                          |  |                                                                          |    |                                                                        |   |             | to  |                          | 
|   |  |                                          |  |                                                                          |    |                                                                        |   |             | to  |                          | 
|   |  |                                          |  |                                                                          |    |                                                                        |   |             | to  |                          | 

---



QuickLinks