smartctl -l farm /dev/sd<n>
They're supposed to be "more trustworthy" than the regular SMART stats.(My two "new" 16TB Exos drives had 0 hours (regular) and ~18k hours (farm) - DOM 04JUN2021 and 07JUN2021. Also, zfs refused to format the drive: 'already formatted as ddf_raid_member'.)