Exhibit 5.1

October 2, 2001

DOT HILL SYSTEMS CORP.
6305 El Camino Real
Carlsbad, California 92009

Ladies and Gentlemen:

    You have requested our opinion with respect to certain matters in connection with the filing by DOT HILL SYSTEMS CORP., a Delaware corporation (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 six hundred forty-two thousand nine hundred four (642,904) shares of the Company's Common Stock, $0.001 par value (the "Shares"), pursuant to the Company's 2000 Amended and Restated Equity Incentive Plan (the "Equity Plan") and 2000 Amended and Restated Employee Stock Purchase Plan (the "ESPP").

    In connection with this opinion, we have examined the Registration Statement, the Equity Plan, the ESPP, the Company's Certificate of Incorporation and Bylaws, as amended, and the originals or copies certified to our satisfaction of 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 Equity Plan or the ESPP, as applicable, the Registration Statement and the related prospectus, will be validly issued, fully paid, and nonassessable (except as shares of the 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,

COOLEY GODWARD LLP

/s/ Thomas A. Coll

Thomas A. Coll