To the best of my knowledge, you can acknowledge faults but alerts should auto clear when the pertaining alert has been resolved.
I'm trying to go through and clear out old alerts in my environment so I can see what alerts truly need action taken. In this particular alert, it says there's no free space left on a datastore and when I look at that specific datastore there's 600gb free. Since I can't cancel this alert..what's my next step?