Error about one disk of 2

Hello there,
I have 2 4TB WD Red HDD in my MyCloudEX2Ultra, with RAID 1 volume.
Today the light of one disk turned from blue to red, and when entering the control panel, one of the disks health is marked as “Bad”, the other one “Satisfying” (respectively “Mauvais” and “Satisfaisant” since it’s french).
What are the immediate consequences (I’m still able to access and read the existing files), and most of all is there a way to fix this without changing the disk? Without losing data?
Thanks for your help

I found this article about replacing an internal drive :

So It seems I have to buy a new HDD, but before I do the replacement, I have to turn off the RAID1 mode in the dashboard? If I do so, will my files be erased?? Or can I just remove the bad disk without turning the RAID1 mode off?

Don’t turn off raid, just replace your bad drive with a new one, same size or bigger size if your device support later size. Once the new drive is replace with the bad one. It should auto rebuild or you can do manual rebuild raid in the WebUI

Yes. No need if turning of the raid. Just replace the same. It will work.

OK, so if I resume : I just turn off the device (hibernate mode), remove the defective disk, put the new one instead, turn the device on, and that’s it. I just wait for the files to be copied in the new disk and everything should be fine and ready

I don’t know what to do: after a power cut in my apartment, when my MyCloudEX2Ultra turned on again, the error disappeared and the two disks are marked as good…
How can I trust, should I change the one that was marked as degraded but is not anymore??

You can try running the full system check in Settings and see if it finds anything.

Step ONE is to do a FULL backup to a 4TB external disk while you have a working system.
and the backup task is NAS to USB

Rebuild takes time and the other disk could fail

I keep a WD MYbook 4TB on each USB port to do backups.

I also put a small fan over the top ex2 Ultra as my rebuilds take over night and the unit gets hot