NetApp OnCommand System Manager 3.1.3 was a vital "off-box" management tool designed for storage administrators to oversee NetApp storage systems via a user-friendly graphical interface. While it was once the standard for managing and early Clustered Data ONTAP environments, it has since reached the end of its official lifecycle. Availability Status: Why You Can’t Find It
Since you can't click a direct "Download" button on the NetApp Support Site anymore, here are your options: netapp oncommand system manager 3.1.3 download
Full management for CIFS/SMB, NFS, iSCSI, and FC/FCoE. NetApp OnCommand System Manager 3