Another newbie question, but I'm trying to obviate the snafu our site experienced in early October. When I look at the server status display and see that list of stuff and the lights are green-and I think green is good. Last month there were reds in a few places that led to the situation I related HERE. We were switched around and life has been good and the lights green for nearly 2 months. Recently I've noticed that one of the lights is flashing yellow and I think- not good. the display section in question is here:
Disk /dev/sda6 (/) 16 %
Disk /dev/sda7 (/tmp) 20 %
Disk /dev/sda8 (/home) 62 %
Disk /dev/sda1 (/boot) 50 %
Disk /dev/sda2 (/usr) 23 %
Disk /dev/sda3 (/var) 48 %
Disk /dev/sdb1 (/backup) 88 %
The emboldened data is followed by the aforementioned flashing yellow light. The % number has been creeping toward 90 where I suspect it will begin to flash red- I think red will be bad. All that said, my question(and remember it's from a rank amateur and newbie) is:
What the heck does it mean and what should or could we be doing about the situation?

If you all can help, well, that would be good!