I have an ASUS Sabretooth 990fx R2.0 motherboard, and I have three HDD's in total. 2 x 250GB Samsung EVO SSD drives and a single WD 1TB HDD.
I had set up my 2 SSD drives in RAID-1 configuration using the on-board hardware RAID, with the separate 1TB drive non-raided and used purely as a data drive.
This configuration was all working well for around the last 3 months or more until I recently started to notice an error on POST saying that the RAID array was in a "critical" state. I booted into the RAID setup and saw that the "LD" definition that I'd previously set up to contain the two SSD drives now only contains 1 drive. The other drive (according to the RAID setup utility) was "failed or disconnected", however other screens within the RAID util show the "disconnected" drive to by perfectly healthy - this is also confirmed by Windows 8.1 itself when I boot all the way into Windows and check the health of the drive from the Disk Management utility.
I do not seem to be able to edit the existing "LD" RAID definition in order to "re-assign" the drive that has seemingly unassigned itself from the array and it would appear that my only option is to delete the LD definition and re-create it, however, I'm assured that this will completely erase the entire disk when I do this, which (given that this is my Windows partition) is something I want to completely avoid.
How can I re-assign the unassigned disk to the existing RAID definition without erasing/losing any data on the currently assigned RAID disk?
Here's a single picture of the LD definition screen within the RAID utility showing the problem:
I've uploaded a gallery of screenshots of the RAID util showing other screens from the utility highlighting the problem in more detail here: https://i.sstatic.net/Gr5xs.jpg