Interesting idea... thanks for sharing.

I have two setups.

1.) A mirror with an attached Tasmota Power Plug that I can turn on and off via curl to spin up an USB-Backup-HD:

  curl "$TASMOTA_HOST/cm?cmnd=POWER+ON"
  # preparation and pool imports
  # ...
  # clone the active pool onto usb pool
  zfs send --raw -RI "$BACKUP_FROM_SNAPSHOT" "$BACKUP_UNTIL_SNAPSHOT" | pv | zfs recv -Fdu "$DST_POOL"

2.) A backup server that pulls backup to ensure ransomware has no chance via zsync (https://gitlab.bashclub.org/bashclub/zsync/)

To prevent partial data loss I use zfs-auto-snapshot, zrepl or sanoid, which I configure to snapshot every 15 minutes and keep daily, weekly, montly and yearly snapshots as long as possible.

To clean up my space when having too many snapshots, I wrote my own zfs-tool (https://github.com/sandreas/zfs-tool), where you can do something like this:

  zfs-tool list-snapshots --contains='rpool/home@' --required-space=20G --keep-time="30d"