In general for regular FAS/AFF Hardware :
1) Once you are 100% sure that the 'Data' stored on the disks are no longer required and you want to ensure that no one can recover the data on the disks then best practices sis to : 'wipe' and 'sanitize*' the disks.
2) Shut down/ Halt -f
3) Power off
4) Inform NetApp via web.
As this is a V-series NetApp : You may have presented 'Array LUNS' (Thirdparty), and may also have Native Disk shelves.
IMPORTANT INFO : For V-Series systems, 'sanitization' is supported only with native disk shelves (not with array LUNs).
Disk sanitization* limitations: (V-Series is mentioned there)
This thread is useful: (For wipe/sanitize)
For Data ONTAP 8.1 and later, enter the following command to enable the disk sanitization feature:
node> options licensed_feature.disk_sanitization.enable on
After the powering off, to inform NetApp about the decomissioning:
Log in to the NetApp Support site (https://support.netapp.com)
1) Select "My Products"
2) Search for the system to decommission in "View Installed Systems"
3) From the pull-down menu of the "Product Tool Set" column for the system, select "Decommission this System".