EXHIBIT 5.1

October 8, 2004
Network Appliance, Inc.
495 East Java Drive
Sunnyvale, California 94089

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by Network Appliance, Inc. (the "Company") of a Registration
Statement on Form S-8 (the "Registration Statement") with the Securities and
Exchange Commission covering the offering of up to 1,300,000 shares of the
Company's Common Stock, $.001 par value, pursuant to its Employee Stock Purchase
Plan and 10,200,000 shares of the Company's Common Stock, $.001 par value,
(collectively, the "Shares") pursuant to its 1999 Stock Option Plan (together
with the Employee Stock Purchase Plan, the "Plans").

In connection with this opinion, we have examined the Registration Statement,
your Certificate of Incorporation and By-laws, as amended, and such other
documents, records, certificates, memoranda and other instruments as we deem
necessary as a basis for this opinion. We have assumed the genuineness and
authenticity of all documents submitted to us as originals, the conformity to
originals of all documents submitted to us as copies thereof, and the due
execution and delivery of all documents where due execution and delivery are a
prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Shares, when sold and issued in accordance with the Plans and the
Registration Statement, will be validly issued, fully paid, and nonassessable
(except as to shares issued pursuant to certain deferred payment arrangements,
which will be fully paid and nonassessable when such deferred payments are made
in full).

We consent to the filing of this opinion as an exhibit to the Registration
Statement.

Very truly yours,

/s/ Wilson Sonsini Goodrich & Rosati, P.C.
- ------------------------------------------
Wilson Sonsini Goodrich & Rosati, P.C.