I have never seen this problem before, and I hope I never see it again.
Replaced failed drive. Rebuild used new spare drive as 'good' drive, overwriting the actual data with the empty contents of the spare.
I don't think that I can recover the lost data at this point, but is there anything that I did to provoke this behaviour so that I can make sure that it never happens again?
Note that I've rebuilt many arrays without incident before this.
Vostro 200 with 500GB RAID1 array.
ICHR BIOS shows array as Degraded with Disk Error(s) on one drive.
Failing drive is removed and replaced with used, but now blank and formatted drive.
On reboot, ICHR BIOS asks whether the new drive should be used to rebuild the array, sets array status to Rebuild and says that the rebuild will complete in the operating system.
Before booting into Windows, I first boot from an Ubuntu LiveCD in order to very SMART status on both drives. They report good.
Reboot and Windows fails to boot.
Swapping original drive back in also fails to boot.
Analysis shows that the array has been rebuilt from the spare, rather than the good drive so that all information has been erased (as the spare was a used but wiped drive).
I have never seen an array rebuild attempt to rebuild the incorrect drive.
If this happened even before the operating system loaded, just in the control I option ROM, the issue might have been an issue with the option ROM itself or a configuration problem. Keep in mind that the only drive that should have been marked as a spare was the recently installed hard drive that was formatted so the rebuild could be done using that spare. The standalone drive with the operating system should never be used or marked as a spare.