Can you teach me this wizardry?

Sure! In Uptime Kuma, add a monitor with type Push. It gives you a URL with a unique token, and the monitor goes into “down” state if nothing calls that URL within the heartbeat interval. Then have a cron (or a systemd timer or whatever) run this on the machine with the drive every 5 or 10 minutes:

use=$(df --output=pcent /mnt/yourdrive | tail -1 | tr -dc ‘0-9’)
curl -fsS -G “http://your-kuma:3001/api/push/TOKEN --data-urlencode “status=up” --data-urlencode “msg=${use}% used” --data-urlencode “ping=${use}”

Ping is of course meant to be response time, but Kuma will graph any number you toss in, so you get a “filled” chart for the drive. I also send status=down once usage passes a threshold. And if the box itself should fall over for some reason, the missing check-ins trigger the alert too.

(I typed this quick on my phone, so please double-check and probably don’t blindly copy-paste)

Thank you! This is dope!