[bitfolk] Need to set up disk space alert.

Hi All, My VPS normally has 45% to 50% disk space free. (7GB) This morning I find that it ran out of disk space on 22nd, and this stopped email alerts getting to me, stopped all the websites from working. All my clients were emailing to ask what was wrong, and those emails were not getting through either. :( I do have fail2ban set up, and uptime robot is checking the websites are up. How can I set up something to alert me of this problem before it becomes critical? Say disk space used over 75%. Many thanks Ian -- Ian Hobson Tel (+66) 626 544 695