In the process of replacing a failed drive in a mirror on TrueNAS Scale, I made a mistake (detached rather than replaced the failed drive) and the vdev is now a single drive and the GUI will only let me add a new drive as a stripe rather than a mirror. It looks the the right way to make it back into a mirror is the use "zfs attach" in the CLI to just attach the new drive to the vdev. However, since I got into this situation by not being thoughtful enough and the answer appears to be zfs generic and from 2014 rather than specific to TrueNAS Scale, I thought I'd ask for a second opinion. Thanks!
Edit: it's not the boot pool
Edit: it's not the boot pool