15 inch Retina MacBook Pro Late 2013, macOS Sierra 10.12.3. I've posted about this before but I haven't found a solution. I have four 3.5 inch hard drives that I use through a Sharkoon Quickport Duo USB 3.0 dock. There's a new WD Green 2TB, an old WD Green 500GB, an old Samsung 2TB, and a brand new WD Blue 3TB. I also use a WD MyPassport 2TB drive, not through the dock. Out of these 5 drives, two have a recurring problem, while the others have never had issues at all: The Samsung 2TB and the WD 3TB have the issue. While the Samsung is an old drive, the WD 3TB is brand new. What happens is that I will do a time machine backup onto the drive, everything is fine, I eject the drive, and then the next time it simply won't mount, and the "fsck_hfs" process runs at 100% CPU for quite a long time (30 mins to a few hours). Then at some point the disk mounts without issues, but there is a folder called "Damaged Files" on it full of hundreds of aliases to random files on the drive. The drive continues to work fine after this, for some time. Then the issue returns. If I quit the "fsck_hfs" process while this is happening, I get an error saying that the disk is now read-only and I must back it up and reformat it as soon as possible. I have done that many times and the problem keeps returning, sometimes after days, sometimes after months. What could cause this? If the dock was faulty, why are my other drives always fine? If the hard drive is failing, why is my brand new WD having the same issue as my old Samsung? Seems oddly unlikely. I've tried installing SMART status drivers but I can't get them to work. I feel like all my data could be lost any day and there is nothing I can do. The data is backed up. It's hard to say when the issue is fixed because it may take weeks or months to show up again. And yes, I always eject the drives properly. The Samsung is used to back up another drive with Backup Buddy, and the WD 3TB is used by Time Machine. Should I return the newer drive while it's under warranty? How can I prove that it has a problem, besides saying "use it heavily for a few months and eventually the problem will probably show up"? Should I buy a new HDD dock? Could it be a software issue? Why does it always happen to the same two drives?