Bad sectors on WD 3Tb Red Drive inside the RAID-1 and why the RAID can't fix them?


Hope it is the right forum category, I did not find any devoted to Red WD disks.

I am running two WD 3Tb Red Drives in an Asustor NAS (RAID-1) and I have encountered some strange behavior.
First, 200 bad sectors were reported by NAS proprietary scanning utility on one of the disks.
Then, to my surprise, I saw that “Current Pending Sector Count” reported by SMART for this disk is just 4, not anywhere close to 200.

I expect the NAS RAID (which runs Linux RAID driver “md”) to rewrite the bad sectors as soon as it encounters them on a read operation (remember, I have a mirrored disk in RAID-1 which is 100% healthy), but I see the same bad sectors again and again, no sector remapping was done at all and when I read the files which include the broken sectors, the NAS hangs for tens of seconds as it encounters broken sectors, and any new copying hangs again and again - no broken sector is fixed and/or remapped.

Any idea what may go on? Is it that my NAS may not willing to rewrite these sectors or is it some feature of WD disk which prevents these sectors to be remapped and rewritten as I may be naively expect? I am suspicious to some extent to WD because it reports very low “Current Pending Sector Count”. But I am not sure at all and generally lost currently. Any idea how I can proceed from here?

Thanks in advance!

PS: of course, I can try to exchange my disk which is on warranty, but suppose it was only one sector broken and the warranty would finish, what then? Throw away a disk just because of one error (which may cause hangs and prevent the RAID to be rebuilt when some other disk goes out)? I am puzzled why the NAS does not recover it.

Hello there,

Try to diagnose the drive with DLG to see if it gives you any errors, you can also try to write zeroes to the drive to see if this helps with the bad sector issue.

Thank you! Eventually, after contacting WD and Asustor I will do that, probably.
Then, I hope, I will understand the situation better.
I still want to see if my RAID is capable of restoring the health of the disk before attempting to reformat it and whether WD may be somehow involved in what looks for me like RAID system misbehavior.

Just wanted to see if there is some ready information on my situation.
May be some cases like mine…