One Synology DiskStation I have at the office said that one oh the hard drive had crashed. After further troubleshooting, I could not find the issue with the hard drive itself. We mounted it in another computer, ran battery of tests; it passed the test.
I formatted the hard drive and mounted it back in the Synology DiskStation. It is possible that it was some kind of software error. I do have the content of this particular Synology DiskStation backed up on another unit.
Oh by the way, I did cover the hole!