Why does Windows say "The disk that your backup is saved on is about to fail"?

On my Windows 8 machine, I have set up backup to a network location on my new NAS (a Synology DS412+).

Backup has succeeded. But in the "Windows 7 File Recovery" section of the Control Panel it says "The disk that your backup is saved on is about to fail":

But I have no other indication that the NAS is about to fail. Logging into the NAS, it reports that the "DiskStation is working well". The NAS is configured with RAID 6. SMART reports no errors whatsoever on any of the four disks. I have used the NAS extensively for several weeks with no issues at all.

Windows event logs of the backup show no warnings or errors.

What exactly is the basis for Windows's diagnose that the disk is "about to fail"? What has it detected?

Solution 1:

Seems likely that it is a bug in windows or it isn't able to read the SMART values properly (more than likely a bug). However there is a third possibility.

Are you looking looking for errors in the SMART error log or have you looked at all the attributes for the drives? It is possible to have a reallocated sector count or other SMART attribute show some warning signs by having a certain value, however until it hits the threshold level then it will not report an error in the error log.

It could possibly be that windows is looking at the SMART values directly and applying its own threshold or other logic/algorithm to it. I think its likely a bug however. You could check however looking at the attributes directly themselves for each drive - if you haven't done so already - rather than just the error log.

For example my drive right now. I'm using GSmartControl - a GUI version of smartmontools: