I have been using a WD EX4100, with 4 WD Red 6TB HDD’s in RAID 5 mode, for five years, no problems at all.
Suddenly, disk nr.1 showed a red light and I got a message that I needed to change the HDD, which I did with a very same WB Red 6TB HDD.
After installing the HDD, the EX4100 started the rebuilding of the volume, this took more than 6 hours.
My problem is that after the rebuilt stopped, I got the message “Rebuilt failure” in the EX4100 display and the red LED for disk nr. 2 lights up steady.
What to do?
Looking forward to hearing good news how to fix this matter!!