Every so often I take a shufti at my NAS, which is QNAP TS253A with 2 x WD Red 3gb HDD using Raid 1. For about 6 months I have been getting messages saying for one of the disks

"Warning [Disk S.M.A.R.T.] Host: Disk 1 Complete Test result: Fatal or unknown error."

At the time, a check of disk health showed the number of bad sectors as 8. This has slowly been falling and the number of bad sectors now stands at 4. So either there is some miraculous recovery taking place, or the bad sector reporting isn't as accurate as it should be.

I don't pretend to understand the workings of hardware to this level of detail, but has anyone else experienced anything similar, and what is your conclusion if so?

How old are the 2 x WD Red 3gb HDD and were they Registered with WD?

Donald wrote: ↑2021-12-23 21:33 How old are the 2 x WD Red 3gb HDD and were they Registered with WD?

They're out of warranty.

The accepted "wisdom" in the IT world for NAS drives is to use matching make and model of hard drive. My experience is that's risky. I've experienced a failure of two WD black caviar drives. They were from the same batch and had the same fault. These days my Netgear NAS has drives from two different manufacturers - it's less risky.

"Warning [Disk S.M.A.R.T.] Host: Disk 1 Complete Test result: Fatal or unknown error."

The message is quite clear - you need to replace the hard disk.

Thankfully with the QNAP it's a hot swap - just let the RAID rebuild overnight.

And we can't say it often enough, RAID is not a backup! Please ensure you have a full backup before proceeding!

Donald wrote: ↑2021-12-24 17:55 "Warning [Disk S.M.A.R.T.] Host: Disk 1 Complete Test result: Fatal or unknown error."

The message is quite clear - you need to replace the hard disk.

Thankfully with the QNAP it's a hot swap - just let the RAID rebuild overnight.

And we can't say it often enough, RAID is not a backup! Please ensure you have a full backup before proceeding!

Could consider getting two, then rotate the spare in periodically so that you have a NAS 'backup' in case one of the others starts going bad...

Donald wrote: ↑2021-12-24 17:55 And we can't say it often enough, RAID is not a backup! Please ensure you have a full backup before proceeding!

Too right. I've never got a RAID to completely restore lost data. Thankfully I have several back ups these days including off site.

tokenbrit wrote: ↑2021-12-24 19:20Could consider getting two, then rotate the spare in periodically so that you have a NAS 'backup' in case one of the others starts going bad...

I've not come across any advice to rotate spares periodically in the manner you suggest. That would involve having to rebuild the RAID overnight every time?

Spend the money on back-up disks and keep one off-site - I have two full back-ups that I regularly rotate.

Maybe a visit to another Forum that has the name QNAP may help?

Returning to the original question, how can it be possible that what was originally 8 bad sectors has now reduced to 4?

On the backup front, I also keep a copy of my ripped music directory on my PC. It's only just over 300GB (for approx 850 albums) so not encroaching too much on my PC disk space.