smartctl -x /dev/ada2

To redirect the output of smartctl -x /dev/ada2 to a file named /mnt/volume0/scr/smartctl_out_ada2.txt I simply type

smartctl -x /dev/ada2 > /mnt/volume0/scr/smartctl_out_ada2.txt

In this example volume0 is the name of a pool, scr is the name of a dataset in that pool and smartctl_out_ada2.txt is the file name proper.

Be prepared that after following this approach permission issues might occur to meet the goal that the file just created is visible in an associated share.

smartctl

https://forums.freenas.org/index.php?resources/hard-drive-troubleshooting-guide-all-versions-of-freenas.17/