Drive failure sustained
Well, one of the drives in the server decided to fail. Fortunately they are all in a RAID 5 array so the server continues to run on degraded mode, and absolutely no data was lost.
As I am running more and more servers on this machine, it's critical that I get some new bigger drives so that I can swap the old ones out as they fail.
However, as long as it's in degraded mode, I have to manually acknowledge the message every time the server passes POST on boot.