Commvault Systems (CVLT) 10-K 2017 FY Annual report

Exhibit 32.1

Certification Pursuant To

18 U.S.C. Section 1350

As Adopted Pursuant To

Section 906 of the Sarbanes-Oxley Act of 2002

In connection with the Annual Report of Commvault Systems, Inc. (the “Company”) on Form 10-K for the period ended March 31, 2017 as filed with the Securities and Exchange Commission (the “Report”), I, N. Robert Hammer, Chairman, President and Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to § 906 of the Sarbanes-Oxley Act of 2002, that:

(1)The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ N. ROBERT HAMMER

N. Robert Hammer

Chairman, President and Chief Executive Officer

May 5, 2017