EX2 Ultra - Replaced 1 disk - RAID Health Degraded after RAID Rebuild

I have a My Cloud EX2 Ultra NAS, almost 6 years old, and got a red light indicating a disk problem. The NAS is set up as a RAID 1 array of two 6TB disks. The dashboard said one of the disks is bad, so I bought a replacement. The bad disk was a 6TB WD WD60EFRX disk and I replaced it with a 6TB WD WD60EFPX disk.

I powered off the NAS, removed the old disk and inserted the new one, powered it back on and the dashboard said: “RAID Health: Rebuilding. Volume_1 is rebuilding.” The rebuild process took almost exactly 14 hours. Immediately after it was completed, the dashboard reported: “RAID Health: Degraded. One or more RAID volumes are degraded.”

The NAS dispatched an email to me, which said: “Volume 1 is degraded. Check the system’s drive status by running Disk Test in Settings / Utilities.” So I ran a “Quick Test”, and the result was:
Disk1 Passed - Quick disk test completed successfully.
Disk2 Passed - Quick disk test completed successfully.

I decided to just reboot the NAS, after which it seems the NAS decided to automatically restart the RAID rebuild process. I left it running again, and 14.5 hours later, there was the same outcome - RAID Health: Degraded.

I’d like to understand exactly what the problem is, and what I should do.

Hi @osullic,

Have you opened a Support Case? If not opened, for more information, please contact the WD Technical Support team for the best assistance and troubleshooting: