Seven. I was expecting it sooner or later, but was hoping for later. It's an old Apple XServe RAID, and replacement drives are no longer available. Fortunately, I have a back-up. Unfortunately, it's on another Apple XServe RAID.
Man, that's scary, as I just setup a RAID5 recently. I am setting up a second identical RAID5 as a backup, but haven't done that yet. Maybe I should use RAID6 instead.
Our current servers are all set up as RAID 6. The Apple ones were retired previous-generation arrays, repurposed for video editing. And they're not SATA - they're 750GB PATA. Not made any more, and way overpriced if you can find any.