query was from 2016, yet perhaps the following shall be of assistance to others as a contribution to FAQ for Bad Sector detected in WD Red on any NAS:
Several situations can give rise to Bad Sectors: if your computer or host device suddenly shuts off due to a power outage or a pulled power cable, it is possible that the hard drive may have shut off in the middle of writing to a sector. In some cases, it is possible for sectors on the hard drive to contain data that does not match their error-correction code — this would be marked as a bad sector. Viruses and other malware that messes with your computer could also cause such system issues and cause bad sectors to develop.
In some cases, bad sectors can be recovered, for examples using WD’s Data Lifeguard Diagnostic (see list Software and Firmware Downloads | WD Support). For SMART testing the ideal is to validate the drive with direct connection using SATA cable to computer/laptop; as the USB cable or enclosure may not be able to pass SMART data through.
You can also try a low-level format. Formatting will delete all the data in your drive (so if possible better to backup your data before proceeding). For information on this process see the link below:
How to low level format or write zeros (Erase) to a WD hard drive or SSHD:
If these attempts do not resolve the issue, or if you still have questions, then prudent option would be to open a support ticket with WD Support. Perhaps also validate if your warranty is still active…
